BUJUMBURA, March 16 (Reuters) - Burundi's last remaining rebel group accused the army of killing five of their commanders and kidnapping five more fighters in clashes that threaten to undermine a shaky peace process.

A military spokesman denied the allegations.

Speaking from Dar es Salaam, Tanzania, a spokesman for the Hutu Forces for National Liberation (FNL) said the fighting took place on Friday in the rebel stronghold of Musigati.

"It's really regrettable, government troops shot dead our members while they were in a meeting," Pasteur Habimana said late on Saturday.

"It's clear that the government has chosen the war option instead of peace talks."

Army spokesman Colonel Adolphe Manirakiza said government troops did not kill any FNL fighter.

"Our troops have just arrested five FNL combatants who were going to hold the population to ransom," he said.

The incident came after mediators announced that FNL leaders would be returning to the central African country by May to finalise a peace deal signed in September 2006.

Talks to implement the peace pact were suspended last July when FNL members walked out after accusing the South African chief mediator, Charles Nqakula, of bias.

On his last visit to Burundi this month, Nqakula said the truce monitoring team, which comprises FNL members, government officials and mediators, would resume work on April 1.

But FNL rebels urged Burundi authorities to grant them an amnesty first, before they join the truce monitoring team.

The FNL insurgency is seen as the final barrier to lasting stability in the coffee-growing nation of 8 million, where more than a decade of ethnic conflict killed 300,000 people. (Reporting by Patrick Nduwimana; Editing by Katie Nguyen and Matthew Jones) (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/ )

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