In Geneva, a commission of inquiry set up by the UN Human Rights Council accused Kadhafi's regime of carrying out systematic attacks on the population, saying that it committed not only war crimes but also crimes against humanity.
While it found fewer reports of violations by the opposition, the commission also found that rebel forces committed acts that constituted war crimes.
"In accordance with its mandate to look also at crimes committed in Libya, the commission has ... reached the conclusion that crimes against humanity and war crimes have been committed by the government forces of Libya," said the commission 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," it added.
The 47-member UN Human Rights Council set up the investigation into suspected crimes against humanity in February after Kadhafi's regime dispatched Libya's army and air force to fire on civilians.
Hours after NATO-led aircraft launched new raids on Tripoli early Wednesday, ambassadors of the military alliance meeting in Brussels decided to renew the mission for another 90 days to late September.
"This decision sends a clear message to the Kadhafi regime. We are determined to continue our operation to protect the people of Libya," said NATO Secretary General Anders Fogh Rasmussen.
"We will sustain our efforts to fulfil the United Nations mandate" to defend civilians from Kadhafi's forces, he said in a statement, adding: "We will keep up the pressure to see it through."
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 Kadhafi from crushing a revolt that began in mid-February.
Wednesday's decision would give individual nations time to prepare their contributions for the next 90 days, a NATO diplomat said.
"There were very positive signs that nations will extend with the appropriate number of resources," the diplomat said.
Oil minister Ghanem, the head of the state-run National Oil Corporation (NOC), told journalists in Rome that he had joined the rebellion, following weeks of rumours and denials about his defection.
"I can't work in this situation so I have left my country and my job to join the choice made by young Libyans to fight for a democratic country," he said.
Ghanem, who has been Libya's representative at the OPEC oil cartel for years, said his country was "moving towards a total block on oil production."
"There is a lot of internal and external pressure in Libya right now... There could be many solutions, including a peaceful solution," he said.
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'S Rasmussen told reporters in Brussels that Kadhafi's departure is only a question of time.
"The question is not if Kadhafi will go but when," Rasmussen said. "It could take some time yet but it could also happen tomorrow."
He added: "I hope to see a solution in Libya before the expiration of the 90-day mandate."
At a news conference in Tripoli, however, Libyan government spokesman Mussa Ibrahim warned the departure of Libya's veteran leader would be a "worst case scenario" for the country.
"If Kadhafi goes, the security valve will disappear," he said.
"Kadhafi's departure would be the worst case scenario for Libya," he told reporters, and warned of "civil war."
Two cars were destroyed in the Benghazi explosion, which occurred in the parking lot of the Tibesti hotel, used by rebel leaders, diplomats and journalists, an AFP correspondent said.
A police officer said a bomb was detonated in one car and the blast damaged a second car parked next to it.
Hotel staff and witnesses said there were no immediate reports of injuries.
The Tibesti is the hotel in which Italian Foreign Minister Franco Frattini inaugurated an Italian consular office on Tuesday.
In doing so, he told reporters that "Kadhafi's regime is finished" and that Italy would fully support the National Transitional Council (NTC), the political arm of the rebellion.
Frattini's comments drew strong condemnation from the Tripoli regime.