Explosions rattled the Libyan capital early Friday as Russia prepared to send an envoy on a shuttle mission to try to broker a negotiated settlement between its Cold War ally and the rebels.
Four explosions were heard at 11:35 pm (2135 GMT) Thursday from the centre of Tripoli, followed by others about 15 minutes later.
Then at 1:45 am (2345 GMT), four powerful blasts shook the district where Gaddafi's residence is located, not far from the city centre.
An army barracks in the same sector had been the target of several raids last week.
Earlier this week, government spokesman Mussa Ibrahim said NATO air raids on Libya had killed 718 civilians and wounded 4,067 since they were unleashed on 19 March and up to 26 May.
In Washington, US military Chief Admiral Mike Mullen pointed to "some signs, certainly in the last few days, that Gaddafi is becoming more and more isolated."
He noted the defection of Oil Minister Shukri Ghanem, who had been a key figure in the regime, along with a group of "young generals" who had also parted with Gaddafi.
Mullen welcomed NATO's extension of its UN-mandated mission to protect civilians through military action until late September.
Russian President Dmitry Medvedev said Moscow will be sending an envoy to Tripoli and the rebels' capital of Benghazi to mediate, the Italian news agency ANSA reported, quoting diplomats.
Medvedev stressed the importance of a negotiated settlement at talks with Italian Prime Minister Silvio Berlusconi in Rome.
"We would like as much as possible for the problem to be resolved through negotiations and not by military means," Medvedev told reporters.
Russia has enjoyed close ties with Gaddafi's regime and abstained from the UN Security Council vote in March that gave the go-ahead for international military action in Libya.
But it has increasingly distanced itself from the regime and at a G8 summit in France last week, Medvedev pledged to ramp up diplomatic efforts to end the conflict.
China, which also abstained in the Security Council vote, announced on Friday that it had opened talks with the rebels.
China's ambassador to Qatar, Zhang Zhiliang, held talks with Mustafa Abdul Jalil of the rebel National Transitional Council (NTC) in recent days, foreign ministry spokesman Hong Lei said in a statement.
"The two sides exchanged views on the Libyan situation," Hong said.
"China's position on the Libyan issue is clear -- we hope that the Libyan crisis can be resolved through political means and that the future of Libya is decided by the Libyan people."
He did not specify when or where the meeting took place.
A commission of inquiry set up by the UN Human Rights Council in Geneva, meanwhile, has accused Gaddafi's regime of carrying out systematic attacks on the population, charging it committed both crimes against humanity and war crimes.
The commission said it "reached the conclusion that crimes against humanity and war crimes have been committed by the government forces of Libya."
The investigative body noted it had received "fewer reports" of abuses by opposition forces but said it "did find some acts which would constitute war crimes."
In Benghazi, NTC vice president Abdelhafiz Ghoga admitted that rebels had committed "violations, twice" as rebels feared terrorist acts by pro-Gaddafi forces in the rebel bastion.
"We feared a fifth column was operating in the city," he said, adding that rebel forces "are trying to treat prisoners according to the Geneva Convention."
Ghoga also announced that rebel forces had detained three suspects in a car bombing that rocked Benghazi on Wednesday but caused no casualties.
"We captured three of the culprits behind the car bomb attack, we are looking for the others," Ghoga said.
Libya's rebel council earlier blamed Gaddafi's forces for the "terrorist attack" that hit the Tibesti hotel, where rebel leaders, journalists and diplomats stay.
Off the Tunisian coast, up to 270 migrants were missing after a ship packed with refugees fleeing Libya and headed for Italy capsized, Tunisian authorities said.
Army and coastguard teams lifted 570 people off the overcrowded vessel after it ran aground and capsized near Tunisia's Kerkennah islands on Wednesday.
But between 200 and 270 were still missing after they tried to scramble aboard a flotilla of rescue boats, Tunisia's official TAP news agency said.