The fighting has displaced thousands of civilians

The Burundi army, struggling for control of Bujumbura, said 28 ethnic Hutu rebels had been killed in a fresh offensive and most of the victims were child fighters aged between 11- and 15-years-old.

An army spokesman said that the rebels had attacked three suburbs east of the city on Sunday before being turned back by government troops.

The capital is on Monday reported to be relatively calm.

The US State Department said that the rebels had fired rockets and mortars at the city and attacked vehicles on the roads in and around the city.

Fighting, which broke out between the Hutu rebel group of National Liberation Forces, (FNL), and the Tutsi-dominated army in the capital a week ago, has claimed about 170 lives, according to the United Nations.

Displaced

Scores of people have been wounded, and more than 15,000 have fled their homes.

Washington has also recommended that private American citizens in Burundi "evaluate their personal security situation in light of the continuing fighting and consider departure while commercial flights remain available".

The Tutsi-led army is fighting for control of Bujumbura

Meanwhile, rebel forces have released 39 civilians who were abducted during clashes in the city last week.

A spokesman for the rebel force, Pasteur Habimana, said that the people had been abducted to protect them from army helicopter gunships which were firing on the area at the time and that they had been released to show that the rebel forces were not the enemies of the Tutsi people.

The ethnic Hutu rebels have been demanding the resignation of the ethnically mixed government, including President Domitien Ndayizeye, a Hutu, who took over the presidency from a Tutsi in April as part of a peace plan.

The assault on Bujumbura during the past week has been the fiercest for years.

Hardline

The UN Security Council issued a statement last week expressing deep concern and calling for an unconditional and immediate end to the attacks.

The FNL is the smaller but more hardline of the two rebel groups opposing the government.

It has refused to take part in peace talks, or to join a ceasefire signed in December 2002 by the main rebel group, the Forces for the Defence of Democracy (FDD) and the government.

A 3,000-strong force of African Union (AU) peacekeepers is in Burundi as part of AU efforts to end the conflict, which has killed an estimated 300,000 people.