It is 6.30 on a dewy autumn morning at an isolated Ananda Marga Pracaraka Samgha retreat in the rolling hills of rural southern Taiwan. Wooden meditation platforms overlook lotus ponds in a landscaped garden, where a wiry, ponytailed Caucasian monk is circling a tree, strumming a guitar and singing a mantra. His long, orange robes flutter in the breeze, his eyes shine with bliss. Repeating the mantra with their arms raised to the sky are 15 or so young people from Taiwan, Hong Kong and Singapore, each of whom has paid the equivalent a couple of thousand HK dollars for what the Indian spiritual group advertises as a five-day yoga and fasting course.

This is day two, and already they are participating in an activity you would not expect to encounter on a typical detox getaway.

Ananda Marga ("path of bliss") has many supporters and many detractors. Founded in 1955 by Prabhat Ranjan Sarkar - whose followers regard the former railway clerk, who died in 1990, as a guru and call him "Baba", meaning father - the group conducts disaster relief work and runs children's homes around the world, including in Thailand and Mongolia, and a primary school in Australia. It also promotes a utopian political philosophy that its devotees believe will succeed capitalism and communism. And it exerts strict control over the orange-robed monks and nuns who are its full-time devotees.

"The group has many features of a cult," says Marsha Low, a 63-year-old former Ananda Marga nun who now lives near Philadelphia, in the United States, and teaches English as a second language.

Ananda Marga emphatically objects to being called a cult or sect, but it has been labelled an "inactive terrorist organisation" by the US Department of Homeland Security's research centre, Start, based at the University of Maryland. This classification relates to events the group was linked to in the 1970s, although Ananda Marga is not viewed as being "actively" terroristic by any government.

Ananda Marga's main East Asian presence is in Taiwan, where it has 13 centres, but it also runs The Meditation Centre, on Lantau Island.

The group has several levels of membership. Some of its followers live in their own homes and do little more than attend meditation classes and help with humanitarian projects. Low's allusion to cultish activity concerns more involved members: Ananda Marga's monks, nuns and civilian devotees known as "local full-time workers".

"It is not an extreme cult, but it does have a hierarchical order and encourages separation from family," says Low, who was with the movement for 18 years until the early 90s, when she became disenchanted with many aspects of it. Low wrote a book about her experiences, called The Orange Robe.

Ananda Marga members would not restrain devotees physically from leaving the movement, she says, but, "In my time, leaders did use psychological means to discourage you from leaving, such as trying to show you would never be happy if you left."

The organisation was banned by Indira Gandhi's government in India throughout much of the 70s. In December 1971, shortly after the Indo-Pakistan War, Sarkar was convicted of the murder of half a dozen former disciples and imprisoned. A retrial of his case in 1978, however, saw him acquitted.

According to the Start website: "Ananda Marga was held responsible for a number of terrorist attacks in the 1970s. The vast majority of these attacks were against Indian diplomatic and business targets abroad, most often in Australia."

In the same year as Sarkar's release, Ananda Marga member Evan Pederick confessed to the bombing of the Sydney Hilton Hotel, which left three people dead. Pederick spent six years in jail, between 1991 and 1997, before his conviction was overturned on appeal due to lack of evidence. Another Ananda Marga member, Tim Anderson, was convicted and served 7½ years behind bars before being acquitted of all charges. No motives were ever established and the case has never been solved.

In 1982, in Bijon Setu, Calcutta, 16 monks and a nun belonging to Ananda Marga were pulled from taxis en route to an educational conference, beaten to death and burned. The massacre, for which a motive was never officially established, occurred in broad daylight but no arrests were ever made.

Another criminal case in which the group's name cropped up was the Purulia arms drop. In 1995, a huge cache of weapons was dropped by air over the district of Purulia, in India's West Bengal, where Ananda Marga is headquartered. A Calcutta district judge ruled in 2000 that the group had had no involvement in the matter. However, Niels Holck, a Danish citizen who stands accused by Indian prosecutors of arranging the arms delivery along with two Hong Kong businessmen (all of them members of Sarkar's organisation), told Britain's Independent newspaper in March 2011 that he was an Ananda Marga member and had been training people at the group's headquarters in unarmed combat.

An Ananda Marga spokesman says in an e-mail that Holck's "statements regarding Ananda Marga are perhaps best left for him to comment on". Holck, who has also used the names Kim Davy and Niels Christian Nielsen, is currently in Denmark and has not been convicted of any crime. The governments of India and Denmark have for years been wrangling over terms for his extradition, to face trial.

These controversies and accusations of cult practices should not, however, detract from Ananda Marga's aid work. It is viewed as a respected humanitarian group and sometimes works alongside the United States Agency for International Development, a government relief organisation. According to its website, Ananda Marga provided food and medical care to the survivors of the 2010 Haiti earthquake. It also participated in relief efforts in India and Indonesia following the 2004 tsunami. And the monks running the retreat in southern Taiwan certainly don't seem to be brainwashing anyone.

The course begins with group singing led by our guitar-playing British monk, who calls himself Dada Yogananda and teaches guests an English song he has composed about the beauty of Taiwan. He has long, wavy hair and sparkling blue eyes, and spends his time at the retreat chatting gently with guests, making sure they are well during the fast. He also leads daily meditation classes. Twice-daily yoga sessions are taught by the other monk present, a 38-year-old Icelandic man calling himself Dada Diiptimanananda, who also leads morning around-the-tree dances. Guests attend daily lectures on subjects such as the benefits of vegetarianism and the healing properties of plants, given by the middle-aged Taiwanese couple who run the retreat, neither of whom wear orange robes.

One hint of Ananda Marga's underlying beliefs stands out. During the hour-long meditation sessions, the 42-year-old Yogananda plays guitar and encourages guests to join him in chanting a mantra of " Baba nam kevalam". The chant is known as " kirtana" and the "baba" referred to is Sarkar, according to Raphael Voix, a French anthropologist who has studied the group since 2002.

"While practising kirtana, disciples visualise their guru as a pure, loving entity," Voix wrote in a 2008 paper. "They stress the love and joy that their guru awards and experience what they call the loving face of the guru."

Yogananda, however, tells his audience the chant means "love is all there is", without going into detail. Those joining in may have no idea they are reciting an incantation dedicated to a deceased railway clerk.

The two dadas running the Taiwanese centre have renounced their birth names. They grow much of their own food and wash their robes by hand in cold water at large sinks outside the main building. The retreat is what Ananda Marga calls a "master unit" and it runs a number of these around the world. They are "intended to approximate a self-sufficient, ideal society", says Suzanne Newcombe, a research officer at Inform, an independent charity chaired by London School of Economics sociology professor Eileen Barker that collects and disseminates information on religious movements.

Yogananda says he is a former fireman and that he joined Ananda Marga 20 years ago, after discovering its meditation classes during a trip to Malta, where he had planned to find work as a diving instructor. He shares his real name with Post Magazine but requests that it not be used in this article.

Ananda Marga monks, nuns and other local full-time workers are "socially isolated and subject to group regimentation and intensive socialisation tactics", writes Helen Crovetto, an independent scholar of new religious movements based in Arizona, in a 2008 paper for Nova Religio, an academic journal produced by the University of California Press. Low corroborates this claim, explaining that as an Ananda Marga nun, she was discouraged from maintaining relations with her family.

"The idea was that your mother was Baba [Sarkar], your father was Baba," she says, adding that she was not expected to think for herself. "Whatever Baba said was the truth, you couldn't disagree. There was no logic, no reason, but compliance with the order." She says devotees wishing to see relatives were encouraged to meet them in the Ananda Marga centre nearest the family home, with other group members present. "It was thought that if you were in contact with your family or friends, you could get pulled back from your spiritual life."

The Ananda Marga spokesman explains: "Having embraced the mission of serving universal humanity [monks and nuns] have renounced conventional family life. Therefore, visits by their family members usually take place at Ananda Marga centres. Such contact is in no way forbidden, but it is formally regulated."

Lorne Dawson, a professor of sociology at the University of Waterloo, in Canada, writes that there are parallels between the methods Sarkar used to set up Ananda Marga and "those of the founders of other successful international contemporary religious movements such as L. Ron Hubbard and the Church of Scientology, and Sun Myung Moon of the Unification Church".

Ananda Marga is a "classic instance of a group based on charismatic authority", meaning Sarkar's, Dawson writes in a report he filed with the Federal Court of Australia last February, when he was acting as an expert witness in a dispute between Ananda Marga and some of its members.

Sarkar cemented his authority over followers by having them follow a treatise providing instructions for "every passage of life", including how to enter a house, how to dress, how to bathe and exercise and even how to wash, according to Dawson's report. The text of the treatise, he writes, says followers must wash "the urinary organ with water" after urination and "when yawning, cover your mouth and at the same time make a snapping sound with your fingers".

Bizarre life instructions aside, Crovetto says Ananda Marga might have the potential to act violently in the future. She writes that it has a budding paramilitary element, which comprises an all-male group named the Volunteers Social Service and a women's division, the Girls' Volunteers. The Ananda Marga spokesman says Crovetto's finding is a "bizarre claim" but, according to the scholar, the volunteer groups are "militias" who "could play a part in future revolutionary activities". Crovetto also reports interviewing a former Ananda Marga member who claimed the volunteers practised with firearms.

The spokesman says the role of the volunteers is to help out at large Ananda Marga functions in India. "Their duty at these large functions, where thousands of members gather, is to guide people, help maintain order."

He does concede, however, that the volunteers are given combat training. "In India, it is quite common to see volunteers guarding private and public premises, and that is also true for Ananda Marga, so it is but natural that such volunteer [sic] train to develop their defensive skills and discipline, but positively without weapons."

Low says she never saw volunteers using guns.

Sarkar had visions of leading a revolution "against exploitative conditions or regimes", writes Crovetto, explaining that he promoted what he called "progressive utilisation theory", which his followers shorten to "Prout" and which calls for an ideal society where everyone has food, clothing, shelter, education and medicine. Ananda Marga followers believe Prout will replace capitalism and communism following a mass revolution. Crovetto writes that Sarkar predicted this revolution would be violent.

"Sarkar was of the opinion that the spiritual evolution of the individual and society was tied to the use of force." She adds that the Ananda Marga founder "believed in the necessity of maintaining military preparedness" for his coming socio-spiritual revolution and "taught that war was inevitable". She also writes that Sarkar "observed that arms were more necessary than the drums and cymbals used for worship" and that "in most cases, popular emancipation is blood-soaked".

"When communism was collapsing in the late 1980s, we really thought, 'Now is the time for Prout'," says Low. "We felt there would be a global collapse and that would create a vacuum that Prout would come in and fill.

"The guru's philosophy was that violent means can sometimes be necessary in times of extreme exploitation."

She repeats, however, that she "never heard of any organised violence taking place".

Low does report occasional violence, however. "[At some point in the late 80s] one Indian didi [the group's term for a nun] did beat us on the back of our calves one time with a ruler as a punishment," she says. In The Orange Robe, Low relates how Sarkar would beat male disciples as part of a religious ritual.

"It was considered a blessing to get a beating from the guru," she writes. "Baba would hit women on the palms."

It does seem a long journey from attending an Ananda Marga yoga class or fasting retreat to becoming an orange-robed devotee, renouncing family ties and promising compliance with a revolutionary philosophy that may or may not be violent. Low says that she and her fellow full-time devotees were "under a lot of pressure" to "produce more whole timers to spread the organisation … so, in yoga classes, you would always hope that some people would become interested in meditation and want to be initiated."

The group spokesman says any claims that Ananda Marga's yoga classes and retreats are recruitment tools are "plainly baseless". He writes: "In our experience, very few of those attending yoga classes are interested in/have time for daily meditation sessions and in adopting a yogic lifestyle."

That said, given the huge variety of yoga styles that are taught in clubs and gyms across Asia, anyone who is not open to joining a socio-spiritual movement may find a regular Hatha or Ashtanga class more appealing.