Thousands of people fled their homes on Tuesday as heavy fighting between Hutu rebels and the Tutsi-dominated army using mortars, rocket-propelled grenades and assault rifles continued for a second day in southern neighborhoods of Bujumbura.
It was not clear how many people had been killed in the fighting, but an army officer, who did not want to be identified, said he had seen more than 50 corpses in the neighborhoods of Musaga, Kinindo and Kanyosha.
Army spokesman Colonel Augustin Nzabampema said government troops had killed 15 insurgents since the fighting erupted early Monday when rebels of the largest faction of the National Liberation Forces, or FNL, attacked the central African nation's capital.
He said two soldiers had been wounded, but gave no details of civilian casualties.
Rebel spokesman Pasteur Habimana said six insurgents had been killed.
The army said it had driven the rebels to the outskirts of Bujumbura late Monday, but the rebels appeared to have moved back into southern parts of the city early Tuesday.
"No one can move, we are stuck inside our houses, only soldiers and rebels can move," Aime Nkurunziza, a resident of Musaga neighborhood, said by telephone.
The insurgents also fired mortars on the capital from the hills surrounding Bujumbura.
The army retaliated by attacking rebel positions with helicopter gunships.
Vice President Alfonse Kadege rejected rebel demands for negotiations. He told civilians at a meeting hall in Bujumbura to use "all necessary measures" to work with the security forces to drive the rebels out of the capital.
Habimana said the rebels would remain in Bujumbura until the Tutsi-dominated army agreed to hold immediate talks.
The rebel attack was the first on the capital since April, when insurgents fired dozens of rockets at Bujumbura.
The main market was closed on Tuesday as thousands of people fled into the town center. Two main highways leading out of the city were also closed.
The civil war erupted in October 1993 after Tutsi paratroopers assassinated the country's first democratically elected president, Melchior Ndadaye, a member of the Hutu majority.
At least 200,000 people, mostly civilians, have died in the conflict.
Despite being in the minority, Tutsis have effectively controlled the tiny nation for all but a few months since independence in 1962.
A transitional administration took office on Nov. 1, 2001 after Hutu and Tutsi political parties signed a power-sharing accord that was supposed to end the war. But the rebels did not take part in that peace process and fighting continued.
Two small rebel factions signed ceasefire agreements last October, but the two main rebel factions, the FNL and the Forces for the Defense of Democracy, which operate in the hills surrounding Bujumbura, have refused to halt fighting.