"The Burundi defence ministry informs the national and international community their patience has some limits," Defence Minister Germain Niyoyankana said in a statement. "Government forces will defend themselves and, if needed, use their legitimate right to pursue FNL rebels to their last hideout."

Last week, the Forces for National Liberation (FNL) seized the head of intelligence services in the northwestern province of Cibitoke and a Bujumbura-based police investigator, saying they wanted to exchange the pair for imprisoned fighters.

And in the latest clashes at the weekend, the rebels killed two soldiers.

The FNL responded to the minister's statement by accusing the government of war-mongering.

"It is the government that wants war, because it has refused to implement the ceasefire agreement," FNL spokesman Pasteur Habimana told Reuters from Tanzania. "The FNL won't be responsible for hostilities launched by the government."

Talks to implement a 2006 peace agreement have been suspended since July, when FNL rebels walked out of a truce monitoring team, objecting to a South African mediator.

The FNL's persistent insurgency is seen as the final barrier for lasting stability in the coffee-growing nation of 8 million people that lost 300,000 in more than a decade of civil war.