Libya's provisional leaders have declared the country liberated from the 42-year rule of Moammar Gadhafi at a ceremony attended by tens of thousands of people in the eastern city of Benghazi.

National Transitional Council leader Mustafa Abdel Jalil and other officials gathered on a podium in Benghazi's Kish Square as Sunday's ceremony began with the singing of Libya's pre-Gadhafi national anthem.

A huge crowd of jubilant Libyans filled the square, waving the red, black and green Libyan flag of the monarchy that Gadhafi overthrew in a 1969 coup, beginning a four-decade long dictatorship.

Benghazi was the hub of the anti-Gadhafi uprising that began in February and ended when he was killed Thursday as provisional government forces defeated his die-hard loyalists in his hometown of Sirte.

International concern about the circumstances of Gadhafi's death offered a contrast to the celebratory mood inside Libya. Rights groups have called for an investigation into mobile phone video that shows provisional government fighters taunting and beating a wounded Gadhafi shortly before he died.

U.S. Secretary of State Hillary Clinton said Sunday that Washington would like to see a U.N. investigation of the killing and supports the investigation that Libya's NTC has pledged to conduct.

In an interview with U.S. television network NBC, she said it is important for a democratic Libya to begin with the rule of law and accountability. She said investigating Gadhafi's death should be a part of that process.

Libyan doctors performed an autopsy on Gadhafi's body in the city of Misrata Sunday and said he died of gunshot wounds to the head and abdomen. It is not clear who fired the shots that killed him. Libyan officials have said the former leader was shot in a crossfire between his loyalists and provisional government forces.

The body was on public display in a commercial freezer in Misrata Friday and Saturday. Details of his burial have not yet been disclosed.

Libya's outgoing provisional prime minister Mahmoud Jibril said Sunday consultations are under way to form an interim government within one month, followed by elections for a constitutional assembly within eight months. Parliamentary and presidential elections would be held within a year after that.

Jibril was speaking on the sidelines of an economic forum in Jordan, where he also announced his resignation to allow new leaders to oversee Libya's transition to democracy.