Roughly 20,000 Myanmar refugees returned home on Tuesday after clashes between government forces and ethnic rebels sent them fleeing across the border into Thailand.
"The heavy shooting in Myanmar stopped a few hours ago, but sporadic gunshots still can be heard," said Chamras Kungnoi, a Thai district chief.
The fighting erupted in response to rigged elections by the military junta that rules the country.
"The reports that we have gathered demonstrate that these elections are deeply flawed, and are fundamentally illegitimate ... unfair and undemocratic," a coalition of dozens of Myanmar media and human rights organizations said in a statement.
The government has been trying to drive the Karen people from their tribal territories for years. The tribe, one of Myanmar's main ethnic minorities, has long sought to gain independence from the military regime.
Patrick Klein of Vision Beyond Borders works with Karen refugees in Thailand. He told CBN News that the government wants the natural resources on their land.
"The people are saying 'No, this is our land. This is the land that was partitioned to us when the British left,'" he said. "And they're saying 'We're not going to give up the land easily, and we're going to fight to protect our villages and our homes.'"
"And it's not just the government targeting the rebel groups," he added. "They're going in and they're killing civilians as well as men, women and children."
About 40 percent of the Karen tribe are Christians, and Klein says troops target Karen believers because of their independence.