It is a vow echoed by Vietnamese officials, who have formally complained about the detention and ill-treatment of hundreds of fishermen in recent years as part of Beijing's assertions of sovereignty.

This is even as they try to negotiate, against the odds, a settlement to their long dispute with Beijing.

Both countries hold claims to the islands based on ancient history. But China, as occupier, is holding all the cards.

And the Paracels are proving an early sticking point in talks between Beijing and Hanoi as they map out a framework to guide a broader settlement of various maritime problems.

Officials close to the talks say Beijing is insisting there is no dispute over the Paracels.

They are under Chinese sovereignty, occupied by China, and there is nothing to discuss. But they remain a thorny issue for Vietnam.

Once occupied by both China and the former South Vietnam, Chinese forces took control in a brief skirmish with the South Vietnamese navy in 1974.

A cluster of reefs, islets and sea-mounts southeast of Hainan and due east of the Vietnam's central coast, the Paracels are rich in fish and tourism potential and are close to disputed oilfields.

They are also highly strategic, sitting astride some of the region's most important shipping routes - a fact not lost on the PLA, which maintains a highly-sensitive listening post on Woody Island in the heart of the archipelago. Talk to veteran Ly Son fisherman Mai Phung Luu, however, and it is clear just how fraught finding a long-term solution could be.

'I believe China wants to make things so difficult for us that we stop going to the Paracels,' Luu says. 'But they can never stop us.

'These are Vietnamese waters, my grandfather fished there, my father fished there and I fish there ... it is our history, and our sovereignty.'

Luu, a 41-year-old father of four, is talking on a rattan mat inside his Ly Son house. On the lanes outside, onions and seaweed are drying, which, along with garlic and fishing, are the island's mainstay.

Little else grows in the volcanic island's sandy soils and the tourism that is sweeping the mainland has yet to reach the isolated reefs of Ly Son. Luu's is fighting talk. Already the actions of Chinese authorities have stopped him fishing.

Detained four times since 2005, he explains his family has paid so much to Chinese authorities to free his boat and crew - wired from Quang Ngai to a Bank of China branch on Hainan Island - that he could not make loan repayments.

A Vietnamese bank has recently repossessed his vessel.

The last time he was captured, in September last year, was the worst.

Held for 35 days on Woody Island, he says he was forced to wear a hood and beaten.

He was also given electric shocks while an interpreter tried to extract confessions that he used dynamite to fish, or was somehow acting on behalf of the Vietnamese government.

He was left with several welts on his back from the electrodes.

'The first thing I told them was not to beat me because I had a wife, children and a mother in Vietnam,' Luu said. 'They asked me instead whether the Vietnamese side had given me weapons or fuel.

'I said no. I come here for the fish....the Paracels are the best fishing around here.'

During detentions, the Chinese seize the catch, remove equipment, fuel and food and sometimes damage the engine, Luu explains.

Sometimes authorities do not seize a boat, but will board it to disable it or take equipment and the catch. On occasions, they beat the crew.

Other times they will simply ram it, other fishermen say.

'Fishing is difficult enough already,' said veteran fisherman and boat owner Dung Quang Thuy.

'They should leave us alone to fish in what are our waters. I urge China to accept this fact.

'The Vietnamese fishermen are not going to give up. The Paracels are their life.'

On Ly Son - the closest point on the Vietnamese coast to the Paracels - it is a familiar cry.

Others talk of turning off their lights at sea, praying before on-board altars and then sailing through the heart of the islands at night.

Regional diplomats have for months pondered just how close the Vietnamese fishermen get to the Paracels.

Ly Son fishermen confirm they get very close, sometimes working within 10 nautical miles of the islands and reefs inside what China claims as territorial waters.

They seek shellfish and edible seaweeds in shallow water as well as fish such as tuna, mackerel and jacks further out, sometimes on trips that can take 35 days.

Significantly, they confirm not only fishing near Triton Island - the nearest to Vietnam - but also Bombay reef and Lincoln Island further east and up to North Reef, a route that passes the Chinese naval base on Woody Island.

Wandering around Ly Son, the Paracels are a constant source of discussion.

As the Vietnamese mainland is just over the horizon, so are the Paracels, in the minds of Ly Son folk. The Vietnamese call the islands Hoang Sa. The struggle of Ly Son, it seems, is being hard-wired into the national propaganda script.

In one corner of the island stands a gleaming new Hoang Sa temple and museum.

Inside are prints of historic maps and documents from the French colonial period and previous dynasties detailing expeditions to the Paracels.

On the mainland, meanwhile, boulevards in Da Nang and Ho Chi Minh City have been recently named Hoang Sa while the islands have been placed under the formal administrative control of Da Nang - even though, at this point, Vietnam holds no actual land to be administered. Near the museum, an elderly land-owner lights incense at a large new tomb. It is dedicated to his ancestor Pham Quang Anh, who led an expedition of soldiers to Ly Son in 1815 on orders from then Emperor Gia Long.

Anh never returned and is thought to be buried on Money Island, which the Vietnamese have named Quang Anh.

Pham Quang Tinh, 76, is not easily dissuaded from his straightforward take on a complex historical dispute.

'During the war, Vietnam and China were friends. China helped Vietnam's liberation and also helped liberate the islands for Vietnam,' he says of the 1974 battle that saw China capture the southwestern Paracels.

'They should now give them back,' he insists, eyes blazing beneath one of the thousands of Vietnamese flags on the island. Officials in Hanoi and the nearby provincial city of Quang Ngai offer similar sentiments.

They insist they encourage their fishermen to avoid working in the Paracels during summer spawning, but are unwilling to weaken Vietnam's sovereignty by acknowledging China's unilateral May to August fishing ban.

They acknowledge calls from the fishermen to be kept safe from Beijing's fishing protection patrols, but are wary of risking open conflict with a much larger Chinese navy.

They also refuse to assist families having to pay 'ransoms' to Chinese officials for the return of their seized boats and crews.

'We encourage them to fish anywhere in Vietnamese waters as is their historic and sovereign rights,' said Quang Ngai fishing official Le Van Son. 'That cannot be stopped.'

But the price is high. Official provincial figures show the number of fishermen detained in the Paracels rose from 155 in 2006 to 400 last year.

After the latest Beijing fishing ban was imposed on May 16, Vietnamese officials are braced for more detentions in the coming weeks.

'We have noticed an improved atmosphere diplomatically in recent months,' one Hanoi official said. 'We can only hope it carries over to the sea as well.'

Speaking privately, Chinese envoys stress there is nothing to discuss over the Paracels. They are Chinese territory, and Vietnamese fishermen infringing on Chinese waters will be dealt with accordingly.

Wang Hanling, a maritime affairs and international law expert at the Chinese Academy of Social Sciences, said the issue of the Paracels was different to the Spratlys further south, claimed by several other countries as well as Beijing and Hanoi.

'China would not discuss sovereignty of the Paracel Islands with Vietnam because it is now under our administration and we insist the islands are an inseparable part of our territory.'

Australian Defence Force Academy academic Professor Carl Thayer, a veteran scholar of Vietnamese issues, said the Paracels issue highlights Vietnam's policy of 'co-operation and struggle' in its bilateral relations with China.

'Vietnam co-operates when both sides can benefit and it struggles when China pursues policies that impinge on Vietnam's important interests,' he said recently.

'The [South China Sea] is an obvious example of Vietnam's struggle against China. The difficulty of this policy is that too much co-operation might entrap Vietnam and give it little room for manoeuvre. And too much struggle may impede co-operation or result in confrontation.'

Dr Sam Bateman, a maritime security senior fellow at Singapore's Nanyang Technological University, said he believed Vietnam was on a 'hiding to nothing' in its approach to the Paracels.

This was due to China's relative strength, both in terms of its occupation and a historic claim that is potentially stronger given inconsistencies from Hanoi during its wartime co-operation with Beijing.

He did note, however, that its pursuit of traditional fishing grounds was an established point under international law.

'It is surprising that the fishermen are so determined to keep on, given obvious economic impacts from losing equipment and fines and so on,' he said. 'I'm not sure they are getting themselves anywhere by carrying out what appears to be some sort of semi-official campaign ... it risks confrontation and hardening positions on all sides. It also raises nationalistic sentiment on both sides, which would make the issue harder to solve through negotiation, which is something the Vietnamese apparently want.'

In a recently published book on China's relations with Southeast Asia, Singapore-based academic Ian Storey warns of the increased risk of another naval clash between Vietnam and China. Noting that the South China Sea will loom large in Sino-Vietnamese ties, Storey writes that 'increasing frictions over fishing grounds and ... energy fields, combined with the changing military balance of power in China's favour, raises the prospect of a Sino-Vietnamese naval clash if the dispute is not managed properly.'

It is a risk, it seems, that the fishermen of Ly Son are prepared to accept.

Additional reporting by Minnie Chan.