Fighters loyal to a failed presidential candidate clashed with army forces in Congo's capital Thursday, U.N. officials and witnesses said. Gunfire and explosions continued through the afternoon.

It was the first fighting in Kinshasa since a leader was installed late last year in the country's first free presidential vote in decades.

Gunfire and heavy explosions started sounding around the home of former warlord and one-time presidential hopeful Jean-Pierre Bemba around noon local time, said U.N. military spokesman Didier Rancher. He said it was unclear what sparked the violence, but confirmed that members of Bemba's guard were fighting soldiers from Congo's army.

The U.N. has 18,000 peacekeepers in the restive Central African country, and regularly patrols the area around Bemba's house, the scene of earlier clashes.

"It didn't appear planned," Rancher said. "It started all of the sudden." Office workers in nearby buildings reported hearing explosions that sounded like heavy arms fire.

Soldiers deployed throughout the city and people could be seen fleeing on foot and in vehicles. Rancher said the U.N. was helping to evacuate people from the area.

A few men wearing the uniforms of Bemba's armed guard could be seen shooting in the street, though most of the fighters were hidden and hard to identify, according to an AP photographer on the scene.

Bemba's guard has refused to disband as promised as part of a deal with the government of President Joseph Kabila.

Bemba, who came in second in last year's vote, initially rejected the election results and his militia took to the streets, clashing with Kabila's security forces. At least two dozen civilians were killed. He gave up his challenge after Congo's Supreme Court rejected his claims of an unfair vote.

Bemba, who recently was elected senator, was allowed keep his personal army — numbering in the thousands — until this month. Last week, his personal guard was expected to register at an army base, where they were to begin their integration into the Congolese security force. But his militia ignored the deadline. A spokesman said at the time that Bemba's security was still uncertain.

Rancher said U.N. officials were contact by telephone with both camps and were attempting to broker a resolution.

Congo's defense minister declined to comment on the fighting. Bemba's representatives could not be immediately reached.