Increased security measures have been initiated at refugee camps near the Thailand-Burma border as tensions within rival Karen rebel groups continues to mount, according to sources along the border.

Officials at the Mae La refugee camp in Thailand’s Tak Province have ordered residents to keep their lights out after dark and to stay alert following skirmishes between the Karen National Union and two splinter Karen groups, the Democratic Karen Buddhist Army and a second group that calls itself the KNU/KNLA Peace Council. Both splinter groups are allied with the Burmese army.

“We have to shut down all the lights at 8 p.m., including all electric generators and even candle lights,” said one Mae La resident.

The order came after reports that the splinter Karen groups were planning an attack on the refugee camp, one of the largest in Thailand with an estimated population of more than 40,000. Relatives of many KNU members live in Mae La camp.

The potential threat to camp refugees has caught the attention of international rights groups. “These civilians face grave threats as the Burmese-government-backed ethnic Karen militias appear to be positioning artillery and heavy machine guns overlooking the Mae La refugee camp,” a statement issued by New York-based Human Rights Watch said.

Burmese communities in the nearby city of Mae Sot have also been alerted to stay indoors after dark for security reasons, border sources said.

Clashes between the opposing groups have increased since the DKBA and its allies launched attacks on KNLA bases near the Thai-Burmese border. At least three of their camps, including the headquarters of the KNLA Battalion 101, located opposite the Thai village of Mae Ramat, have been captured by the splinter Karen rebels.

The threat to the Mae La camp is “real,” KNU General Secretary Mahn Sha told The Irrawaddy on Friday, adding that the rival groups have turned against civilians who did not support their break from the KNU.

Despite elevated security concerns, no clashes were reported on Friday, according to Mahn Sha.