BUJUMBURA, June 8, 2008 (AFP) - Burundi's top rebel leader warned Sunday his fighters would only regroup as part of a peace process if a political and military agreement is struck with the government.

'Regroupment is a principle that must be respected but I believe that a political and military accord is needed' in bids to end a 15-year civil war, rebel leader Agathon Rwasa told a news conference at Bujumbura airport.

'We need to know about our party's and fighters' future beforehand.'

Rwasa, leader of Burundi's last active rebel group, the National Liberation Forces (FNL), spoke before boarding a flight for South Africa for a three-day meeting with African Union, EU, UN and Burundian officials on the peace process.

He returned from exile on May 30, four days after his group inked a truce with the government, raising hopes of an end to the war.

He said the regroupment issue had not been broached yet but must be discussed if the truce is to work out.

The government accused the FNL on Saturday of still massively recruiting fighters in defiance of a 2006 ceasefire accord.

But Rwasa rejected this on Sunday as 'absolutely wrong', accusing the government of arbitrary arrests.

Diplomats in Bujumbura said South African President Thabo Mbeki would meet with Rwasa during his visit and possibly organise a meeting between the rebel and Burundi's President Pierre Nkurunziza who is already in South Africa.

Rwasa's return from Tanzania last month marked a new step in moves to definitively end the civil war that has plagued the impoverished central African nation since 1993, leaving at least 300,000 people dead.

He was born in 1964 and joined the FNL -- the country's first Hutu rebel group -- 20 years ago before eventually taking over its leadership in 2000.