TRIPOLI (AFP) - US military chief Admiral Mike Mullen said Thursday that Libyan leader Moamer Gaddafi was increasingly isolated as Russia announced it would send envoys to Tripoli and Benghazi to mediate the conflict. The United Nations, meanwhile, denounced war crimes committed both by Gaddafi's forces and the rebels vying to oust the Libyan strongman. "There are from my perspective some signs, certainly in the last few days, that Gaddafi is becoming more and more isolated," Mullen told reporters in Washington. Mullen pointed to 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. He also welcomed NATO's extension of its UN-mandated mission to protect civilians through military action until late September. "I think from my perspective, and I've engaged with the commanders on this, that we're going to be okay until September," he said. An AFP correspondent said a series of blasts overnight shook the Libyan capital, the target of intensive NATO air raids in the past few weeks. In its latest operational update released on Thursday, NATO said its jets had bombed a vehicle store and surface-to-air missile launcher in the vicinity of Tripoli. Earlier, NATO Secretary General Anders Fogh Rasmussen told reporters that Gaddafi's departure was only a question of time. "The question is not if Gaddafi will go but when," Rasmussen said. "It could take some time yet but it could also happen tomorrow." 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 Italy's Prime Minister Silvio Berlusconi in Rome on Thursday. "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 a UN Security Council vote in March that gave the go-ahead for international military action against Libya. But it has increasingly distanced itself from the regime and at the G8 summit in France last week Medvedev pledged to ramp up diplomatic efforts to end the conflict. A commission of inquiry set up by the UN Human Rights Council in Geneva accused Gaddafi's regime of carrying out systematic attacks on the population, charging it committed not only crimes against humanity but also war crimes.