Former DR Congo rebel leader Jean-Pierre Bemba has taken refuge in the South African embassy in Kinshasa after fighting erupted in the capital.
Mr Bemba has challenged his defeat in October's election
At least 10 people have died during street clashes between the army and militiamen loyal to Mr Bemba - who lost a presidential election last October.
He has rejected government calls for his private security force to disarm.
The UN Security Council has expressed "serious concern" over the fighting and has called for an immediate ceasefire.
"Bemba has taken refuge in the South African embassy as a temporary measure," South African foreign ministry spokesman Ronnie Mamoepa said.
Fighting ebbed in the Congolese capital overnight, but the BBC's Arnaud Zajtman in Kinshasa reports that violence flared once again in the early hours of Friday.
In neighbouring Congo-Brazzaville, the government is preparing for an influx people fleeing the DR Congo violence.
DR Congo's oil reserves were bombed during the violence and thousands of civilians were still caught in the middle of the fighting, our reporter says.
Mr Bemba's militiamen have reportedly taken control in part of Kinshasa's business district. However, the cars of government soldiers were able to move on the main street of the strategic area.
Mr Bemba's personal armed guard are believed to number 200 men
According to eyewitness reports at least seven civilians and three soldiers have been killed but given the intensity of the fighting the final count could be much higher, our correspondent says.
Earlier, UN peacekeepers evacuated more than 450 civilians from areas affected by the fighting to its Kinshasa headquarters using armoured personnel carriers.
Some 15,000 UN troops - the world's largest peacekeeping force - are present in DR Congo.
On Thursday night, Mr Bemba called for a ceasefire and negotiations with the government.
However, the country's information minister said that since the government was democratically elected last year there was no reason for fresh talks.
Mr Bemba's personal armed guard is believed to number some 200 men, according to a 2006 estimate from the UN mission in Congo.
Mr Bemba, who was a vice-president in the transitional government and is now a senator, is entitled to 15 policemen for his protection.
Under an agreement signed ahead of the election, the winner of the presidential poll is committed to guarantee the loser's security.
But Mr Bemba's Movement for the Liberation of Congo (MLC) party says their leader is in danger and wants talks about the terms of these agreements.
Last year's elections were DR Congo's first democratic elections in more than 40 years.
President Joseph Kabila won 58% of the vote compared to Mr Bemba's 42%. Mr Bemba contested the results, but his challenge was rejected by a court.