MAE SOT, Thailand - Myanmar's biggest rebel group will soon abandon a stronghold on the Thai-Myanmar border after weeks of fierce fighting with government and rival Karen forces, a rebel commander said on Thursday.

The Karen National Union (KNU) will adopt guerrilla tactics rather than waste lives trying to defend the base in eastern Myanmar, KNU Commander Kyaw Ny told reporters by telephone.

"The withdrawal from our 7th Division base does not mean we are defeated. It is a tactical redeployment. We also do not want to kill our fellow Karens in this battle," he said.

Myanmar troops and their allies from the breakaway Karen Democratic Karen Buddhist Army (DKBA) launched a new offensive against the KNU on June 3, driving some 3,000 Karen refugees into Thailand, the Thai army says.

The KNU has been fighting for independence in the hills of eastern Myanmar for the last 60 years. The conflict is one of the world's longest running insurgencies.

Rebel leaders say the latest offensive is part of the military regime's campaign to eliminate all opposition ahead of promised multi-party elections in 2010.

The trial of Myanmar opposition leader Aung San Suu Kyi, who faces up to five years in jail if convicted of violating her house arrest, resumes next week.

Critics say the trial is aimed at keeping the Nobel laureate and National League for Democracy (NLD) leader in detention ahead of next year's polls.

The Karen, an ethnic minority of about 7 million people, have been fighting for independence since 1949, one of the world's longest-running guerrilla conflicts. They are one of a handful of rebel militias not to have signed a ceasefire with the junta.

In February last year, KNU leader Mahn Sha Lar Phan was shot dead at his home in a Thai border town in an assassination blamed on the regime and its Karen allies.

Myanmar has been under military rule of one form or another since 1962, during which time it has been riven by dozens of ethnic guerrilla wars, funded in part by revenues from opium sales from the notorious "Golden Triangle".