Forced recruitment by the Myanmar military has driven 3,000 Karen refugees into Thailand, and is likely lead to a bigger exodus soon, the Karen Human Rights Group said Tuesday.

The group, which has been monitoring the plight of Karen refugees on the Thai-Myanmar border since 1992, blamed this month's exodus from Pa-an district in Myanmar's Karen State on a forced recruitment drive combined with a military offensive led by the pro-junta Democratic Karen Buddhist Association (DKBA).

"The DKBA has started calling itself a border security force," said Stephen Hull, a researcher for the Karen Human Rights Group. "There is a push by the Myanmar government to increase the size of the force so they have been recruiting since late 2008."

The recruitment drive, combined with an offensive against the remnants of the Karen National Liberation Army (KNLA), has forced many Karen families to flee to Thailand.

"We fear there will be more and more refugees soon," researcher Poe Shan said.

The DKBA is a breakaway faction from the Karen National Union (KNU), which has been waging a struggle for the autonomy of the Karen State in western Myanmar since 1948.

The KNLA has been pressed hard this year by the DKBA, which is backed by the Myanmar army, and is on the verge of defeat, according sources at the border.

There are already an estimated 100,000 Karen refugees in camps in Thailand, and thousands more working as migrant labourers in the country.

Myanmar's military regime, using the DKBA, has been trying to wipe out the Karen resistance since 1992, displacing tens of thousands of people in the Karen State.

Past tactics have included forced labour, village burning, heavy taxation, looting and rape. The DKBA, which is slated to become the area's security force in the aftermath of next year's election, is now also forcibly recruiting conscripts, the sources said.

Fighting in the Per Her of Pa-an district in Karen State started on June 2 and intensified Friday when some 900 Myanmar and DKBA troops launched multiple 81-millimetre mortars at the camp near the Thai-Myanmar border, Karen sources said.

The fighting forced 3,000 people from Per Her and surrounding villages to flee, joining another 700 who had fled the fighting on June 4.