THE HAGUE, Netherlands -- The International Criminal Court will investigate Libyan leader Muammar al-Qaddafi and his inner circle, including some of his sons, for possible crimes against humanity in the violent crackdown on anti-government protesters, the prosecutor said Thursday.

Luis Moreno-Ocampo said Qaddafi's security forces are alleged to have attacked "peaceful demonstrators" in several towns and cities across Libya since Feb. 15, and he identified Qaddafi and several commanders and regime officials as having formal or de facto command over the forces that may have committed crimes.

Moreno-Ocampo vowed there would be "no impunity in Libya."

Armed with unusual authority from the U.N. Security Council, Moreno-Ocampo acted with unprecedented haste to launch an investigation, partly to warn Libyan officials against any continued slaughter of civilians.

He said the court was using the opportunity "to put them on notice: If forces under their command commit crimes, they could be criminally responsible."

He also warned that leaders of the Libyan opposition, who have seized weapons from the Libyan military, could be investigated if allegations were raised against them.

"No one has the authority to attack and massacre civilians," he said.

Moreno-Ocampo mentioned only Qaddafi by name, but identified seven people by their positions to be investigated. They were the commander of the 32 battalion, the head of Qaddafi's personal security, the national security adviser, the director-general of the external security organization, the spokesman of the regime, the head of the security forces and the minister of foreign affairs.

Qaddafi's son Khamis commands the elite 32nd battalion and another son, Muatassim, is the national security adviser. The foreign minister is Moussa Koussa. It was not immediately clear if his son Seif al-Islam Qaddafi, a public face of the regime who often seen was as the heir apparent, was included in the prosecutor's list.

Moreno Ocampo said he did not yet know how many officials would be in the final list of suspects.

Qaddafi has denied using violence against demonstrators, whom he described as agents of Al Qaeda. International media have been unable to witness the worst of the reported incidents.

Contacting former Libyan officials and army officers, Moreno-Ocampo said he spent the last six days gathering information on the structure of authority in Libya to find those in control of the forces. He also has appealed for video and photographs of any alleged atrocities.

"We are not saying who is responsible yet," he said. "Today is the start of the investigation."

He said it could take several months before he presents his case to judges and requests arrest warrants.

It is the second time the court, which was created in 2002 as the world's first permanent war crimes tribunal, has investigated a sitting head of state. Sudan's Omar al-Bashir has been indicted on three counts of genocide for attacks in the western Darfur region, but Bashir has rejected the charges against him and refused to surrender to the court.

The U.N.-backed court has no power to execute its own arrest warrants, and must rely on national authorities to take suspects into custody and extradite them to The Hague.

The Security Council's unanimous resolution asking the criminal court to look at the Libyan case was a breakthrough for the court, which has struggled for acceptance. Five of the council's 15 members, including three permanent members, have refused to sign or ratify the court's founding treaty, and the decision last Saturday was the first time the U.S. had voted affirmatively for the court on any issue.

The referral of the Sudan case passed in 2005 with a U.S. abstention.

But the United States insisted on including a provision in the Libyan resolution to protect Americans from investigation or prosecution, presumably in the event U.S. forces later get drawn in to the Libyan conflict.