|Thousands of Myanmar refugees have crossed into Thailand amid the clashes [Reuters]
The two main pro-democracy opposition parties in Myanmar have conceded defeat in the country's much-criticised general election.
The announcements came on Tuesday, after the biggest military-backed party, the Union Solidarity and Development Party (USDP), said that it had taken 80 per cent of available seats in the nation's first poll in 20 years.
"We took the lead at the beginning but the USDP later came up with so-called advance votes and that changed the results completely, so we lost," Khin Maung Swe, leader of the largest opposition party the National Democratic Force, told the Reuters news agency.
The second-largest pro-democracy party, the Democratic Party, also conceded defeat.
A senior USDP official said that the party had taken a broad victory, although official results are yet to be released.
Al Jazeera's special correspondent reports on the difficulty in ascertaining the true will of the people
He said that the USDP had picked up 75 to 80 per cent of seats.
Complaints have been lodged with the election commission by at least six parties claiming that state workers were forced to vote for the USDP in advance balloting.
Meanwhile, some refugees who were forced to flee to the Thai border town of Mae Sot have begun heading back to Myanmar after the government said that battles had ceased.
Fighting between Myanmar government troops and ethnic fighters had sent at least 20,000 people fleeing into neighbouring Thailand.
Clashes were reported on Monday in the military-led nation at key points on the border with Thailand, leaving at least three people dead and 10 others wounded on both sides of the frontier.
The clashes follow a demonstration by the fighters over Sunday's general election as well as attempts to force ethnic minority troops to join a border guard force - which would put them under state control.
The ongoing civil war has wracked parts of Myanmar since independence in 1948 and observers say the state's determination to crush ethnic anti-government fighters appeared to have increased in the lead up to the election.
In the heaviest fighting, Karen fighters reportedly seized a police station and post office on Sunday in the Myanmar border town of Myawaddy.
Sporadic gun and mortar fire continued into Monday afternoon.
Al Jazeera's Marga Ortigas, reporting from the Thai border town of Mae Sot, said that a stray rocket propelled grenade crossed into Thailand, injuring five people.
"The clashes appear to be between a faction linked to the Democratic Karen Buddhist Army (DKBA) and government-backed troops," Ortigas said.
"This faction has said it did not support the ceasefire the DKBA signed with the Myanmar government, and have reiterated that they want their own autonomy."
Our correspondent also said refugees from Myanmar who crossed the border into Thailand feared government troops would shoot them for failing to vote on Sunday.
Zipporah Sein, the general secretary of the Karen National Union (KNU), said fighting broke out between up to 300 DKBA soldiers and government forces.
"We don't know definitely but I think last night the army sent over more troops, they negotiated and the DKBA retreated but this morning they were blocked by army trucks and then it started," she said.
||29 million eligible voters
||40,000 polling stations
||3,071 candidates from 37 political parties
||82 independent candidates
||494 seats in the two-chamber parliament
||665 seats spread among 14 regional parliaments
Myanmar, also known as Burma, drew international criticism over Sunday's vote with Barack Obama, the US president, saying the election was stolen.
"It is unacceptable to steal elections, as the regime in Burma has done again for all the world to see," Obama, currently on a tour of four Asian nations, said in a speech to India's parliament in the capital New Delhi, on Monday.
Europe and Japan also condemned the conduct of the poll as state TV reported that voters "freely and happily" cast their ballots.
In many constituencies, the poll was a two-way battle between the USDP and the National Unity Party (NUP), which is the successor to former leader Ne Win's party and also closely aligned with the military.
A senior government official, speaking on condition of anonymity, said voter turnout was estimated at more than 60 per cent but that the results from the whole country could take one week.
Ban Ki-moon, the UN secretary-general, said voting conditions had been "insufficiently inclusive, participatory and transparent".
Than Nyein, chairman of the National Democratic Force, created by former members of the National League for Democracy (NLD), led by detained opposition leader Aung San Suu Kyi, said the election was marred by irregularities.
"It's very different from our expectation because of foul play," he told the AFP news agency.
"We have our evidence. Some candidates complained ... because there was vote cheating."
|Aung San Suu Kyi, detained opposition leader, supported a boycott of Sunday's election [AFP]
With no specific time given for the release of election results, western powers were labelling the vote as a "missed opportunity".
But some saw the poll as a small step towards democracy after almost five decades of military rule, with opposition parties confident of success in areas they did contest.
However, with 25 per cent of the seats in parliament reserved for military appointees regardless of the outcome, the two main pro-military parties needed to win just 26 per cent of the remaining seats to secure a majority.
Al Jazeera's correspondent in Myanmar added that despite opposition groups running in the polls, electoral advantages had been skewed towards the USDP.
The NDF said some people had complained that they were told by the USDP there was no need to vote as their ballots had already been collected.
More than 29 million people were eligible to vote but it remains uncertain as to how many actually cast ballots.
After the election, attention is now turning to whether the government will release Aung San Suu Kyi on Saturday, when her current term of house arrest ends.
The Nobel Peace Prize winner led the NLD to power in 1990 but the result was never recognised by the ruling generals. She has been detained for most of the last 20 years and supported a boycott of Sunday's election.
Source: Al Jazeera and agencies