Thousands have been forced to flee their homes

About 170 people have been killed since rebels began attacking Burundi's capital on 7 July, say the United Nations.

Shelling by Hutu rebels of the Forces for National Democracy (FNL) is the fiercest assault on Bujumbura for years.

In figures revealed at a Security Council meeting behind closed doors, the UN office in Bujumbura also said that between 6,000 and 7,000 civilians who have been displaced have sought refuge in schools and other public buildings in the city.

The offensive on Bujumbura has been strongly condemned by UN Security Council members which has called for the unconditional and immediate end to the attacks.

Night-time curfew

Rockets have been targeted right at the heart of the city and 80% of the city is now without electricity.

State-run radio announced a curfew from 2100 local time (1800 GMT), saying it had been prompted by continuing security problems.

The future make up of the Tutsi-dominated army is crucial

The rebels have their camps in the mountains just outside the city and usually their attacks are directed at the vulnerable suburbs.

The Burundian army says it has killed 15 rebels in Bujumbura.

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 even under the new Hutu presidency of Domitien Ndayizeye, who came into power at the end of April.

Burundi's leader said then that his top priority was to bring peace.

The rebels say they will sustain their attacks to pressure the government of President Ndayizeye to start negotiating with them.

Fighting has continued in Burundi despite a largely disregarded ceasefire signed in December 2002 by the main Hutu rebel group, the Forces for the Defence of Democracy (FDD), and the government.

The FNL did not sign the agreement.

A 3,000-strong force of African Union (AU) peacekeepers is in Burundi as part of AU efforts to end the decade-old conflict between the Tutsi-led army and Hutu rebel militias that has killed an estimated 300,000 people.