The Democratic Republic of Congo has issued an arrest warrant for an opposition leader, accusing him of treason, as his gunmen battle the army.
Some of Mr Bemba's guards have abandoned their positions
Militiamen loyal to ex-rebel leader Jean-Pierre Bemba are losing ground to government forces in the capital.
Mr Bemba, who lost elections last year, has immunity as a senator but the government says this may be stripped.
He has taken refuge in the South African embassy but the government wants him handed over.
Last year's election - the first free poll in four decades - passed off peacefully, raising hopes of an end to years of conflict and mismanagement.
The BBC's Arnaud Zajtman in the capital, Kinshasa, says that in some areas, the army seem to be gaining the upper hand, with Mr Bemba's guards running away, abandoning their uniforms and surrendering to UN peacekeepers.
"Bemba committed treason in using the armed forces for his own ends," said Congolese government spokesman Toussaint Tshilombo.
But Mr Bemba denied trying to oust Mr Kabila and said his house had been attacked four times.
"I feel they want to kill me," he told the BBC.
South Africa's deputy Foreign Minister Aziz Pahad urged all sides to stop fighting but did not say whether Mr Bemba would be handed over to the Congolese authorities.
The United Nations Security Council has expressed "serious concern" over the fighting and has called for an immediate ceasefire.
In neighbouring Brazzaville, capital of Republic of Congo, the government is preparing for an influx people fleeing across the river which separates the two cities.
DR Congo's oil reserves were bombed overnight and thousands of civilians remain caught in the middle of the fighting, our reporter says.
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.
A Nigerian diplomat has been injured in the fighting and is trapped in his residence.
Earlier, UN peacekeepers evacuated more than 450 civilians from areas affected by the fighting to its Kinshasa headquarters using armoured personnel carriers.
Some 17,000 UN troops - the world's largest peacekeeping force - are stationed in DR Congo.
Mr Bemba challenged his defeat in October's election
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.
A deadline for Mr Bemba's guards to disarm expired this week but he wants additional security guarantees before they lay down their weapons.
Mr Bemba's personal armed guard is believed to number some 200 men, according to a 2006 estimate from the UN mission in Congo.
As a former vice-president in the transitional government, Mr Bemba is entitled to 15 policemen for his protection.
Under another agreement signed ahead of the election, the winner of the presidential poll is committed to guarantee the loser's security.
President Joseph Kabila won 58% of the vote compared to Mr Bemba's 42% in an election run-off last October.
Mr Bemba gained a majority in the west, including Kinshasa, while Mr Kabila won a landslide in eastern areas.
Mr Bemba contested the results, but his challenge was rejected by the courts.