|Thousands of Myanmar refugees have crossed into Thailand amid the clashes [Reuters]
Fighting between Myanmar government troops and ethnic fighters has sent at least 10,000 people fleeing into Thailand a day after the military-led nation held a much-criticised election.
Clashes were reported on Monday 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, Myanmar's first in 20 years, as well as attempts to force ethnic minority troops to join a border guard force - which would put them under state control.
A simmering 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.
Myanmar, also known as Burma, drew international criticism over Sunday's vote with Barack Obama, the US president, saying the election was stolen.
Al Jazeera's special correspondent reports on the difficulty in ascertaining the true will of the people
"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 New Delhi.
Europe and Japan also condemned the conduct of the poll as state TV reported that voters "freely and happily" cast their ballots.
State media, featuring photos of Than Shwe, the country's ruling general and other senior leaders voting, announced the "winners" in 57 constituencies, 55 of which were contested by just one candidate, more than two thirds of those with the Union Solidarity and Development Party (USDP).
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."
Abhisit Vejjajiva, the Thai prime minister, has said that ethnic minority clashes with the military in eastern Myanmar could continue for months.
He also said that the country was ready to provide humanitarian assistance as refugee numbers continue to rise.
"It is possible that it will carry on during the next three months, particularly during the transition from the current government to an elected government," Abhisit told reporters in the Bangkok, the Thai capital.
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.
Two opposition parties accused the USDP of illegally collecting advance ballots.
||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
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.
International condemnation of the polls continued to grow, with Hillary Clinton, the US secretary of state, saying Washington would maintain "rigorous sanctions" against the Myanmar government.
The electoral process was "severely flawed, precluded an inclusive, level playing field, and repressed fundamental freedoms," Clinton said.
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.