It also said the mission found some evidence of war crimes by opposition forces.
“The Commission has reached the conclusion that crimes against humanity and war crimes have been committed by the Government forces of Libya,” the Human Rights Council 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 Geneva-based council said.
The commission's report -- handed to the council on Wednesday -- is based on their meetings with 350 people across the country, thousands of pages of documents and photos as well as hundreds of videos, the council said.
The experts examined allegations of excessive use of force, extrajudicial killings, torture, interferences with freedom of expression, sexual violence and attacks on civilians and the use of child soldiers among others.
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 Qaddafi 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 fulfill the United Nations mandate” to defend civilians from Qaddafi’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 Colonel Qaddafi 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.
Mr. Rasmussen told reporters in Brussels that Colonel Qaddafi’s departure is only a question of time.
“The question is not if Qaddafi 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 Qaddafi goes, the security valve will disappear,” he said.
“Qaddafi’s departure would be the worst case scenario for Libya,” he told reporters, and warned of “civil war.”
Libyan Oil Minister Shukri Ghanem announced in Italy meanwhile that he had resigned and left Libya to join the uprising against Colonel Qaddafi “to fight for a democratic country.”
Mr. Ghanem, the head of the state-run National Oil Corporation (NOC), told journalists in Rome that he had joined the rebellion, following weeks of rumors 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.
“There is a lot of internal and external pressure in Libya right now... There could be many solutions, including a peaceful solution,” said, Mr. Ghanem, who has been Libya's representative at the OPEC oil cartel for years
Italy's foreign ministry denied any role in arranging Mr. 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.
Mr. Ghanem, who is one of the most senior Libyan officials to have defected, said he still saw some possibility of a peaceful settlement to decide the fate of Gaddafi's 41-year-old rule. But he added that the last time he saw Gaddafi was “months ago”.
Mr. Ghanem, whose whereabouts had been unknown for several days, also said oil production in Libya is coming to a halt because of the international embargo.
Now in its fourth month, the Libyan conflict is deadlocked, with rebels unable to break out of their strongholds and advance towards Tripoli, where Gaddafi appears to be firmly entrenched.
Rebels control the east of Libya around the city of Benghazi, the third-biggest city Misrata, and a mountain range stretching from the town of Zintan, 150 km (95 miles) south of Tripoli, towards the border with Tunisia.
(Sara Ghasemilee, an editor at Al Arabiya English,