Myanmar troops and their allies in the Democratic Karen Buddhist Army, a local militia, launched an offensive against Karen National Union strongholds in early June, shelling their camps and sending more than 4,000 civilians fleeing into Thailand.

The KNU says Ler Per Her camp in Myanmar, which sheltered internal refugees, was abandoned last week _ prompting one of the largest refugee movements into Thailand in recent years _ and that government forces were trying to overrun five Karen positions in the area of the camp.

The Free Burma Rangers, which helps displaced people in eastern Myanmar, said Wednesday that government troops had overrun three of those positions.

KNU spokesman David Thaw maintained that the guerrillas have largely repelled the offensive and "killed or wounded 148 soldiers" in recent weeks. Only five Karen have been killed in the fighting, he said.

A spokesman for Myanmar's military government did not respond to a request for comment, and it was impossible to independently verify the claims because reporters cannot access the area.

The KNU has been fighting for more than 60 years for greater autonomy from Myanmar's central government, but its strength has dwindled over the past decade due to army offensives and divisions within its ranks.

Some 100,000 mostly Karen refugees already shelter in camps in Thailand after fleeing counterinsurgency operations in the past two decades, while aid agencies say nearly half a million others are internally displaced inside eastern Myanmar.

The latest refugees were taking shelter about 60 miles (100 kilometers) north of Mae Sot, a border town that is 240 miles (380 kilometers) northwest of the Thai capital, Bangkok.

Human rights groups as well as the United Nations have long accused the Myanmar government of torture, killings and rape of Karen civilians in their attempts to stamp out the insurgency. The military regime denies such allegations.