U.N. troops opened fire on rioters Thursday, killing two, as a mob broke into their base and tens of thousands of protesters overran Congo's (search) capital, outraged at the United Nations (search) over the rebel takeover of an eastern city.

In an attempt to defuse the crisis over the capture of Bukavu, rebel commanders said they would withdraw their troops from the strategic city and return it to the control of the United Nations and the central government.

The fall of Bukavu to commanders once allied to Rwanda (search) threatens to plunge the Central African country back into civil war. President Joseph Kabila accused Rwanda — Congo's chief adversary in the 1998-2002 war — of backing the Wednesday capture of the city.

Rwanda denies any role, and U.N. officials say they have not seen any evidence of Rwandan involvement. A U.N. spokesman said he could not confirm whether rebel forces had begun the promised withdrawal from Bukavu.

In the capital, Kinshasa, protesters blamed Kabila's government and the 10,800-strong U.N. peacekeeping force for allowing the fall of the city on the other side of the sprawling country — and they vented their anger in the largest protests since 1997.

Masses of people flooded the streets, marching on the main U.N. headquarters and other facilities, burning tires and looting shops.

"The state is dead!" protesters armed with wooden clubs cried. "We will punish the United Nations ourselves."

Mobs broke down the door at the U.N. logistical base outside the city center, streamed inside and began to loot, U.N. Congo mission spokesman Hamadoun Toure said.

U.N. troops guarding the building opened fire, killing two protesters and wounding another, Toure said. "We were left with no choice," he said.

Congolese security forces opened fire — apparently in the air — to hold back thousands of protesters who besieged the main U.N. headquarters in the heart of Kinshasa, trapping U.N. workers inside. Rioters hurled rocks and sticks at the troops.

The demonstrators denounced Kabila's weak government, calling the president a traitor. "Kabila is an accomplice of Rwanda," some protesters cried.

In Bukavu, more than 900 miles northeast of the capital, the two renegade commanders — Gen. Laurent Nkunda and Col. Jules Mutebutsi — said they would withdraw their forces. Nkunda pledged his loyalty to Kabila's government.

"We shall withdraw to reorganization centers to assure the transitional government that we are not opposed to it," Nkunda said.

The two officers are Congolese Tutsis who belonged to Rwanda-backed rebels during the civil war but became commanders in Congo's army after the peace process began and a transitional government was formed.

They say they launched their revolt Wednesday because the regional military commander assigned by the Kinshasa government — Brig. Gen. Mbuza Mabe — was persecuting members of a Tutsi community, the Banyamulenge.

Nkunda said Thursday he had already ordered 300 of his soldiers to leave Bukavu and that the remaining troops would leave later in the day. He said he was in talks with U.N. peacekeepers to have them take control of the city.

Mutebusi also told The Associated Press that he is pulling out his troops. He said Congolese military police loyal to him and Nkunda would patrol the town along with U.N. peacekeepers.

U.N. spokesman Sebastien Lapierre, though, said he could not confirm the plan.

"Apparently (Nkunda) said he would remove some troops. At this stage I'm trying to confirm if this is true, how many troops will be withdrawn, and where they will be (based)," Lapierre said in Bukavu.

U.N. officials estimate that Nkunda has between 2,000 and 4,000 troops, while Mutebutsi controls several hundred fighters.

"The withdrawal is intended to pave the way for the governor appointed by (Kabila's) government to come take up his post," Nkunda said. "It is also intended to allow the government to appoint a new military commander in the region."

U.N. medical workers at a Bukavu clinic treated three women — including a 15-year-old and a pregnant woman — for severe injuries after being raped early Thursday.

Residents threw stones at U.N. vehicles and threatened to lynch U.N. workers in Bukavu's Kadugu neighborhood, which was especially hard hit by the renegade soldiers.

Nkunda accused Mabe loyalists of causing unrest in the city and insisted his forces were trying to keep security.

In the northeastern city of Kisangani, students demonstrated and tried to set fire to a U.N. post and two U.N. vehicles. Congolese soldiers fired shots into the air to disperse the protesters.

Rwanda and the rebel commanders in Bukavu denied the Congolese president's accusations that Rwanda was behind the uprising in the city.

Speaking on state-run Radio Rwanda Thursday, Foreign Minister Charles Muligande said Kabila's allegations were unfounded and that Kabila was hiding his shame that his troops had been defeated.

U.N. officials in the region also said they had no evidence of any Rwandan involvement.

Rwanda was Congo's chief adversary in the civil war, which drew in the armies of six nations and killed an estimated 3.5 million people through violence, famine and disease.

The war started when Rwanda and Uganda backed Congolese rebels against Congo's government, accusing it of failing to contain ethnic militias behind the 1994 Rwandan genocide.