ICC Chief Prosecutor Fatou Bensouda told the Security Council that serious crimes were committed by members of Moammar Gadhafi's government during civil war in 2011.
"We are currently engaged in the process of documenting the most serious of those crimes and documenting the current activities of those officials who were most responsible for them," she said.
NATO forces intervened during the conflict in response to attacks by pro-Gadhafi forces on civilians. Bensouda said rebel forces were suspected of committing crimes against some ethnic groups affiliated with Gadhafi's regime.
Gadhafi's son, Saif al-Islam, and former intelligence chief Abdullah al-Senussi are in Libya awaiting trial. Senussi faces Libyan charges of playing a role in the massacre of more than 1,000 prisoners in 1996. Both men are wanted by the ICC for crimes committed during the 2011 war.
"What happens with Libya's perpetrators is a page in the history books of international justice, no matter where those investigations and prosecutions take place," Bensouda said.
Libya claims the right to try both men in the national justice system.