The International Criminal Court says the killing of civilians in Libya followed a pre-determined plan prepared before the latest anti-government upheaval began.
The Libyan unrest started in mid-February, two months after the beginning of protests in nearby Tunisia that led to the ousting of president Zine el Abidine Ben Ali on 14 January.
It prompted Western forces to begin air raids on Libya to enforce a United Nations-sanctioned no-fly zone and protect civilians from attacks by troops loyal to leader Muammar Gaddafi.
ICC's prosecutor Luis Moreno-Ocampo announced in March that the court was investigating Colonel Gaddafi, three of his sons and other members of his regime for crimes against humanity, AFP reports.
"In January, after the revolts in Tunisia, they started to prepare to face problems in Libya, they organised themselves," he said.
The UN Security Council referred the situation in Libya to the ICC in February, saying "the widespread and systematic attacks currently taking place (in Libya) against the civilian population may amount to crimes against humanity".
Mr Moreno-Ocampo has said a request for an arrest warrant will be made a few weeks after he informs the UN Security Council of his findings on 4 May.
