Myanmar has been in turmoil since a February coup ousted Aung San Suu Kyi's elected government, sparking huge protests among civilians and renewing clashes between the military and ethnic rebel armies in its border regions.

The Karen National Union (KNU) -- one of Myanmar's largest rebel groups in its east, which has tussled with the military for decades -- has been locked in renewed conflict with the army since the coup.

In May, state-run media accused fighters from one of the group's armed wings, the Karen National Defence Organisation (KNDO), of a May 31 massacre of 25 construction workers -- an allegation the KNU had said it would investigate.

Spokesman Padoh Saw Taw Nee confirmed Saturday that the KNDO's head, General Ner Dah Bo Mya, and his subordinate Lieutenant Saw Ba Wah have been "suspended temporarily".

"According to the Geneva Conventions, even if they are our enemies, we just arrest them, you cannot kill like that," he said.

"We stand firmly on our commitment to the Geneva Conventions and the international community, and we have to deal with this carefully."

The decision -- made on Monday by KNU leaders -- will inject more discord within the rebel group, whose political divisions over the handling of the junta have spilled out in recent months to the public.

Padoh Saw Taw Nee defended the suspension as "part of our procedures".

- 'We cannot mingle with the devil' -

But General Ner Dah Bo Mya blasted the decision, saying that the KNU's political leaders had refused to hear the KNDO's side.

He said fighting had broken out as his troops were arresting military intelligence personnel, alleging an ambush by Burmese soldiers who deployed mortar artillery against them.

"During the armed conflict, the soldiers didn't take care," he told AFP, adding that he did not want to cooperate with the investigation because "they didn't talk to me".

"Our grand leader and politicians should side with us instead of working with the enemies," he said.

"We cannot mingle with the devil."

Myanmar's border regions are a patchwork of territories and alliances held by more than two dozen rebel groups, most of whom have fought with the military for more autonomy and resources.

Since the coup the KNU has clashed sporadically with the Myanmar military along the Thai border.

In March its fighters seized a military post and the army retaliated with air raids, the first in more than 20 years in Karen state.

The group has also condemned the military for the power grab, and provided shelter to dissidents working to oust the State Administration Council -- as the junta has dubbed itself.

Nearly 890 people have been killed by the junta's security forces since February 1, according to a local monitoring group.