Preparations are under way for the expected release of Burma’s detained opposition leader Aung San Suu Kyi, officials said on Wednesday, after the Army's proxies claimed a landslide election win.

Suu Kyi, who has spent most of the past two decades locked up, had her detention extended by 18 months in August 2009 over a bizarre incident in which an American man swam uninvited to her lakeside home where she is under house arrest.

"We haven't got any instruction from superiors for her release yet. But we are preparing security plans for November 13," a government official told AFP on condition of anonymity.

The democracy icon's term of detention is due to end on November 13, although some fear Burma’s military regime, headed by junta chief Senior General Than Shwe, may find an excuse to extend it.

Another official, who also did not want to be named, said: "We don't have the order yet. It will be at the last minute." Suu Kyi's lawyers say the current period of detention started with her imprisonment on May 14, 2009, and they expect her to be freed on Saturday.

The Nobel peace prize winner swept her National League for Democracy (NLD) to power in the country's last elections two decades ago, but the party was never allowed to take power.

The NLD was disbanded after boycotting Sunday's poll — widely dismissed by the West for being a sham with Suu Kyi sidelined. The party's decision not to participate deeply split Myanmar's opposition.

Some former NLD members bolted to create the National Democratic Force (NDF), which was meeting on Wednesday to weigh its next move after the junta-backed Union Solidarity and Development Party (USDP) claimed it won 80 per cent of the seats.

The largest opposition party running, the NDF appeared to have secured only about 10 per cent of the more than 160 seats it contested and accused the USDP of cheating through its collection of advance votes.

"I'm very sorry because these acts could further harm the dignity of our country," party chairman Than Nyein said Tuesday. "Our country has lacked dignity in the world so we wanted to restore our pride with a fair election."

The Democratic Party, the second largest pro-democracy group, appeared to have won not a single seat in the national legislature, but chairman Thu Wai said they "cannot do anything".

"We are planning to discuss with other parties after we collect the data. We will try to work not only with the NDF but also with other parties," he said. One quarter of the seats in Parliament are already reserved for the military, which together with its proxy looks set to have a comfortable majority for passing laws and electing the president.

A new constitution requires parliament to convene at least once a year. "Opposition groups have charged that this is an omen that the Parliament will be convened only once a year," said Thailand-based Burmese analyst Aung Naing Oo.

Thai officials said on Wednesday that 20,000 refugees had returned to Burma, after crossing the border into Thailand after fighting broke out between ethnic rebels and government forces a day after the poll.

The state-run New Light of Burma said three civilians were killed and 20 injured, blaming "terrorists... Committing various subversive acts to disrupt State's stability, community peace and tranquility and rule of law".

It said one police officer was killed and four soldiers wounded in a separate border clash. English-language newspaper ran little about the poll, aside from a piece about China welcoming the "smooth general election".

Burma’s Southeast Asian neighbours have also welcomed the vote as a "significant step forward" but Western allies have largely criticised the vote, led by US President Barack Obama. UN secretary-general Ban Ki-moon said it was "insufficiently inclusive, participatory and transparent".