There are “reasonable grounds” to charge Moammar Gaddafi’s security forces with having committed war crimes and crimes against humanity during their crackdown on Libyan protesters, according to the chief prosecutor for the International Criminal Court.

The prosecutor, Argentine lawyer Luis Moreno-Ocampo, has said in a report to the U.N. Security Council that his investigators have established preliminary but “credible” estimates that at least 500 to 700 civilians have been shot to death by government forces. Moreno-Ocampo said he intends in the next few weeks to submit his first application for arrest warrants against officials “most responsible for crimes against humanity” in Libya since Feb. 15. The abuses, he noted, are ongoing.

The prosecutor’s report also raises concern that anti-government mobs or armed opposition forces may have engaged in “the unlawful arrest, mistreatment and killings of sub-Saharan Africans perceived to be mercenaries.”

In anticipation of the report’s official release Wednesday, Libya’s Deputy Foreign Minister Khaled Kaim said Moreno-Ocampo’s case was based on “unverified information or video footages reproduced or Photoshopped by some amateur photographers.” He said his government had hosted a fact-finding mission from the U.N. Human Rights Council and was prepared to host a follow-up visit.

The Security Council voted unanimously in late February to authorize the court to conduct an investigation into alleged excesses by Gaddafi’s troops, who launched a brutal crackdown on protesters demanding democratic reforms. It is the second time since the court’s inception that the ­ council has voted to trigger such a probe.

In 2005, the council backed a probe into alleged war crimes in Darfur attributed to the Sudanese government. The court has since issued an arrest warrant for President Omar Hassan al-Bashir on a charge of genocide, but Sudan has refused to surrender him.

Under the terms of the Rome Statute, the treaty that established the court, Libya should be given the chance to investigate allegations of war crimes and crimes against humanity on its own. But the report says that government initiatives — including the forming of a panel of inquiry by one of Gaddafi’s sons, Saif al-Islam Gaddafi — have been inadequate.

The report raises the prospect that Gaddafi and members of his family and inner circle could be charged with war crimes.

“The shooting at peaceful protestors was systematic, following the same modus operandi in multiple locations and executed through Security Forces,” the report says. “The persecution appears to be also systematic and implemented in different cities. War crimes are apparently committed as a matter of policy.”

The death toll in Libya has been hard to determine because of widely divergent estimates on both sides of the country’s conflict. As of March 15, Gaddafi estimated that 150 to 200 people had died, half of them members of government security forces. The rebels’ Transitional National Council says that as many as 10,000 people have died and that more than 50,000 have been injured, the report says.

The prosecutor’s report says that it has been difficult to determine the precise number of victims because bodies have been removed from the streets and doctors have been prohibited from documenting “the number of dead and injured in the hospitals after the violent clashes began.”

Correspondent Simon Denyer in Tripoli contributed to this report.