Burundi's largest former rebel group has withdrawn from President Domitien Ndayizeye's unity government.
The incorporation into the army of FDD rebels is not affected
The group - Forces for the Defence of Democracy (FDD) - has accused the government of not abiding by a peace accord to end a decade of civil war.
FDD leader Hussein Rajabu told the BBC that six months after agreeing to a ceasefire, the FDD was not adequately represented in the administration.
Bu the said the decision did not mean a return to war.
Correspondents say the group's decision to join the government last November raised hopes that peace would return to Burundi, after fighting between rebels from the Hutu majority and the Tutsi-dominated army left some 300,000 people dead.
"This is obviously a dramatic development which is
symptomatic of very serious divisions within the Burundian government about the way forward," Jan Van Eck, a Burundi expert in South Africa, told Reuters news agency.
Troops from an African peacekeeping mission are currently in Burundi to protect senior officials from the Hutu-based FDD, while their fighters are integrated into a new army and police force.
Mr Rajabu suggested the planned integration of the FDD into the existing Tutsi-led army would be unaffected for now.
"We have no problem with the people we used to fight, with the army," he told Reuters.
"The problem is with the politicians, with the political parties."