"This week's fighting is the worst in the capital since Joseph Kabila became the Democratic Republic of Congo's first democratically elected president last year."
Bemba, a former warlord who came in second in the presidential run-off, has rejected the election results.
He promised to disband his army after the election but has repeatedly missed deadlines to do so, most recently last week.
Refusing to disarm, his fighters took to the streets, clashing with Kabila's security forces, Barsoum said.
Bemba, a Congolese senator, has taken refuge in the South African embassy compound and denies plotting a military overthrow of the government.
In telephone interviews from the embassy he has insisted that he was innocent.
|Bemba has sought refuge in the South African|
Bemba said: "I think this is yet another way to try and neutralise me, because they didn't manage to kill me and decapitate the opposition."
He said he wants security guarantees before he orders his men to lay down their weapons and accused the government of starting the violence.
A warrant has been issued for Bemba's arrest on charges of high treason.
South Africa, which has been a contributor to the DR Congo's peace process, said in a written statement that it was "deeply concerned" about the violence in the Congolese capital.
It said: "The South African government appeals to all the forces in the DRC to immediately cease hostilities and begin negotiations to allow the democratic processes to continue."
Eye witnesses said there were dozens of bodies riddled with bullets throughout the city's streets, most of them thought to be soldiers from both sides. Some reports said 60 people or more, most of them soldiers, have been killed since Thursday.
Alain Akouala, a government spokesman, said that during the height of the fighting, mortar rounds landed as far as 4km away in Brazzaville, the capital of the neighbouring Republic of Congo, damaging the home of that country's defence minister.
The Spanish embassy in Kinshasa was also hit, stores and private homes were looted and an oil refinery was set on fire.
The UN peacekeeping mission in Congo welcomed the return of order on Saturday, but said it "deeply regrets the fact that force was used in order to resolve a situation that could and should have been settled through dialogue".