"I think the way in which Mr Gaddafi was killed creates suspicions of ... war crimes," ICC prosecutor Luis Moreno-Ocampo told reporters.
"I think that's a very important issue," he said. "We are raising this concern to the national authorities and they are preparing a plan to have a comprehensive strategy to investigate all these crimes."
Under pressure from Western allies, Libya's National Transitional Council has promised to investigate how Gaddafi and his son Mo'tassim were killed.
Mobile phone footage showed both alive after their capture. The former Libyan leader was seen being mocked, beaten and abused before he died, in what NTC officials said was crossfire.
Reuters
