(CNN) -- About 10,000 people have fled from Myanmar into Thailand to escape fighting between Myanmar government forces and a splinter group of rebels of the Democratic Karen Buddhist Army, military and border officials told CNN on Monday.
The rebels and Myanmar forces clashed Sunday and Monday over control of the town of Myawaddy, which sits across the Moei River from Mae Sot, Thailand. The Thailand-Burma Friendship bridge connects the two towns.
Lt. Col. Vannathit Wongwai, commander of Thailand's 3rd Region Army, said Myanmar military officials told him they had retaken control of Myawaddy late Monday afternoon after bringing in 500 reinforcements to battle the Karen splinter group.
At least five Myanmar refugees and five Thais were injured in the fighting, the officials said. Shells fell on the Thai side of the border, but the Thai military did not return fire, military officials told the Bangkok Post.
According to a report on the website Burma Election Tracker, the clashes began when DKBA militia members who had been employed as government border security troops rebelled because the Myanmar military was forcing people to vote at gunpoint in this weekend's election.
"In order to win votes in the elections, [the junta] is bullying and forcing people to vote. But the people want to boycott [the vote], so the soldiers are holding them at gunpoint and our troops had to intervene and take sides with the people," the website report quotes Brig. Gen. Na Kham Mwe, head of the breakaway DKBA faction, as saying.
Polls closed Sunday in Myanmar's first election in 20 years, which critics have called a facade of democracy put forth by the ruling military junta.
Opposition parties were either limited in the candidates they could put on the ballots or boycotted the election altogether. The junta did not allow international monitors.
U.N. Secretary-General Ban Ki-moon denounced the voting conditions in a statement Monday, calling them "insufficiently inclusive, participatory and transparent."
"Myanmar authorities now have a responsibility to turn the conclusion of the first election in 20 years into a new beginning for the country and its people," Ban said. "Consistent with their commitments, the authorities must demonstrate that the ballot is part of a credible transition towards democratic government, national reconciliation and respect for human rights."
The Karen ethnic minority in Myanmar is divided into two main groups, Buddhists who support the ruling junta and Christians who do not. Those behind Monday's clashes have split from the pro-junta group.