An ex-leader of Burundi's former rebel National Liberation Forces on Monday claimed responsibility for a weekend attack near the capital and announced the creation of a new FNL faction.
"We have decided to take up arms against the government under the new banner of FNL-Ubugabo burihabwa," Aloys Nzabampema, the group's "chief of staff", said in a statement.
His statement claimed responsibility for a Sunday evening attack on a military base on the outskirts of Bujumbura in which, he said, rockets were fired towards the airport.
Burundi army spokesman Gaspard Baratuza acknowledged an attack "far from the airport" but said it was done by a "group of bandits" who were quickly repelled.
A diplomatic source told AFP that the 300-500 fighters who have taken to the bush pose a threat to the country's stability and that "they may not worry Bujumbura, but they have the power to destabilise."
As the last active rebel group in Burundi, the FNL laid down its arms in April 2009 after a 2006 ceasefire agreement that ended 13 years of civil war in the tiny central African country.
The conflict, in which 300,000 lives are believed to have been lost, pitted Hutu rebels against an army that was then dominated by the Tutsi minority.
In 2010, former FNL leader Agathon Rwasa withdrew from the country's electoral process, disappeared and was soon followed by Nzabampema.
In Monday's statement, Nzabampema claimed he was taking up arms again because of "a policy of extermination of FNL members" by Bujumbura's CNDD-FDD regime, a former Hutu rebel group and now a political party, that has been in power since 2005.
Rights groups as well as the UN's Security Council have voiced concern over a series of "extra-judicial killings" in the country since 2010.
Observers have feared that Burundi could slide back into full-blown civil conflict.© ANP/AFP