The decision by US President Donald Trump to slam shut the doors of America to the citizens of seven Muslim-majority countries has been widely perceived as one that will inflame anti-US sentiment around the world.

Opponents of arguably the most controversial US leader to occupy the White House argue that the move – introduced in an opening flurry of presidential executive orders – say it will have the opposite effect to its stated intention of making Americans safer; instead it will work as a recruiting sergeant for extremist groups like Islamic State and al-Qaeda.

It fuels concerns among regional counterterrorism officials that the US-backed war machine currently encircling Islamic State (IS) could spawn a greater terror network in Southeast Asia and elsewhere, one made up of fleeing militants seeking a safe haven in their home countries.

In October last year, Jeremy Douglas, the representative for the United Nations Office on Drugs and Crime (UNODC) in Southeast Asia and the Pacific, told This Week in Asia that the threat posed by foreign terrorist fighter returnees was “real and imminent”.

“Increasing military pressure on [IS] in Syria and Iraq is now expected to result in more returnees including many that will want to pursue violent jihad in the region,” Douglas said.

The UNODC estimates there are 516 Indonesians, 100 Filipinos, 100 Malaysians and two Singaporeans fighting in Syria and Iraq. If even just a handful of these battle-hardened fighters return to home soil, they have the potential to orchestrate large-scale attacks either by working in small cells or as “lone wolves”.

That warning was followed last month by a reiteration that the threat of a “spectacular’’ attack on a high-profile target – specifically the world’s richest gaming hub Macau – was being underestimated.

It wasn’t the first time the Hong Kong-based risk consultancy Steve Vickers and Associates had suggested terrorists might be considering a “spectacular attack on a soft target such as a mall in Australia or casino in Macau”.

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A Vickers report in 2016 suggested that Macau’s gaming sector offered a “nexus of Chinese, American and Jewish interests” that a terror group would find particularly appealing. Las Vegas Sands tycoon Sheldon Adelson and Wynn Resorts chairman Steve Wynn – two big players in Macau – are both Jewish.

In its latest risk report for 2017, Vickers reiterated his concerns about Macau: “An understated threat is terrorism. Macau represents a unique agglomeration of Chinese, American and Jewish interests, engaged alongside triad societies [Chinese organised crime] in an activity [gambling] that Islamists deem sinful. Worse, the city is vulnerable.”

Sources have also told This Week in Asia that in recent months security checks have been stepped up on visitors arriving in the casino hub who are travelling on or carrying passports from Islamic countries and whose last port of call was the Philippines.

Vickers said: “The Philippines is definitely a weak link because of its relatively porous and multifaceted coastline, plus the obvious threat of a support network for radical Islamists in the country’s restive southern regions.’’

A security insider has also told This Week in Asia that Macau’s international airport, which connects it to key regional cities – is considered a “weak link” when it comes to the gaming hub’s security.

A warning came in August 2015 when Indonesian authorities arrested six men suspected of plotting a terror attack on Singapore’s Marina Bay district, the home of Las Vegas Sands’ Marina Bay Sands integrated resort.

Police said the six planned to fire rockets at Marina Bay from Batam, an Indonesian island across the Strait of Singapore. The men were detained following a series of raids on multiple locations, including one where weapons were found.

The arrested men were said by police to be part of the [email protected] terrorist group. They are believed to have had organisational help from Muhammad Bahrun Naim, an Indonesian currently fighting in Syria with IS. Bahrun is suspected of involvement in January’s terror attack in Jakarta that killed eight people. The Jakarta Post reported that Indonesian authorities were acting on a tip from their Singapore counterparts. Singapore Defence Minister Ng Eng Hen posted a Facebook message saying everyone “should assume that there may be more plots, other terror cells on the lookout for ways and new munitions to penetrate our defences”.

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Marina Bay is a popular hub for international tourists, as it offers a mix of residential, commercial, hotel and entertainment options, and Marina Bay Sands is one of its most visibly striking features. There is no evidence that the casino was a specific target of the plot.

Vickers, however, said predictions of an attack on a “spectacular” target like Macau in the wake of Trump’s so-called “Muslim ban” could be overly dire.

While standing by his assessment last month, Vickers, who formerly served in the Criminal Intelligence Bureau of the Hong Kong police, said: “The terrorists often strike when they are on the back foot and feel they are being ignored. It might just be that the recent events in the United States have been a boost to their public relations machine.’’