Nato air raids shook Tripoli on Thursday as the UN denounced crimes against humanity and war crimes during fighting between Muammar Gaddafi’s forces and rebels seeking to topple the Libyan strongman.

Libya’s rebel leadership meanwhile welcomed the defection of former oil minister Shukri Ghanem and urged other regime officials to follow suit.

A series of six blasts at around 12.35 AM (2235 GMT on Wednesday) were followed by several more a few minutes later in the Libyan capital, the target of intensive Nato air raids in the past few weeks, an AFP correspondent reported.

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.

Government spokesman Mussa Ibrahim said on Tuesday that Nato air raids on Libya had killed 718 civilians and wounded 4,067 since they were unleashed on March 19 and up to May 26, but Nato said there was nothing to verify the claim.

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, saying that it committed not only crimes against humanity but also war crimes.

While it found fewer reports of violations by the opposition, the commission also said rebel forces committed acts that constituted war crimes.

The commission has “reached the conclusion that crimes against humanity and war crimes have been committed by the government forces of Libya,” it said in a statement.

“The commission received fewer reports of facts which would amount to the commission of international crimes by opposition forces, however, it did find some acts which would constitute war crimes.”

The 47-member UN Human Rights Council set up the investigation into suspected crimes against humanity in February after Gaddafi's regime dispatched Libya’s Army and air force to fire on civilians.

Ex-oil minister Ghanem announced in Rome on Wednesday that he had left Libya to join the rebellion and “fight for a democratic state.”

He added however that he was not working with the rebels' National Transitional Council (NTC) based in their capital Benghazi in Eastern Libya.

The NTC said Ghanem’s defection was saluted by the whole of Libya and called on others to follow his example, adding that Libyans should unite with the rebels to finish off the Gaddafi regime.

“The NTC salutes the latest defection from the Gaddafi regime, that of oil minister Shukri Ghanem,” Abdul Hafiz Ghoga, vice-president of the rebel group which holds the East of Libya, said in a statement.

“In recent days and weeks we have witnessed an acceleration in defections from the Gaddafi regime, which has no legitimacy, credibility or future,” he added.

Ghanem, Libya's longtime representative at the Opec oil cartel, had said in Rome his country was “moving towards a total block on oil production.”

Italy’s foreign ministry denied any role in arranging Ghanem’s presence in the country but welcomed the announcement, after eight Libyan military officers this week announced their defection at a press conference in Rome.

Nato, whose current campaign expires on June 27, has intensified its air raids in recent weeks with daily strikes on command and control bunkers in Tripoli to prevent Gaddafi from crushing a revolt that began in mid-February.

Nato ambassadors meeting in Brussels on Wednesday decided to renew the mission for another 90 days to late September, giving individual nations time to prepare their contributions.

“This decision sends a clear message to the Gaddafi regime. We are determined to continue our operation to protect the people of Libya,” said Nato secretary general Anders Fogh Rasmussen.

“We will keep up the pressure to see it through.”

Rasmussen told reporters that Gaddafi’s departure is 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 on Friday."

At a news conference in Tripoli, however, Ibrahim warned the departure of Libya's veteran leader would be a “worst case scenario” for the country and could trigger “civil war.”

“If Gaddafi goes, the security valve will disappear,” he said.