Muammar Gaddafi's forces have pounded Misrata's lifeline port, killing at least five people, as the International Criminal Court's chief prosecutor said "thousands" have died in the insurrection against the Libyan strongman.
Rebel spokesman Jalal al-Gallal said loyalist shelling on Wednesday killed at least five people in the port, where the International Organisation for Migration (IOM) said a ship managed to evacuate about 800 people, including stranded migrants and the wounded.
The United States appealed to Gaddafi's regime to stop attacking the port and allow international organisations to send in humanitarian aid and evacuate civilians from the rebel-held city.
ICC chief prosecutor Luis Moreno-Ocampo said the murder and persecution of civilians was still being carried out by Gaddafi's regime and that he would seek arrest warrants for three people he did not name.
With the airport in government hands, the rebels are entirely dependent on supply by sea.
The port has been repeatedly shelled by Gaddafi's forces and few vessels are docking, resulting in worsening food shortages.
But the IOM said the chartered ship Red Star One had evacuated some 800 people despite shelling and shooting in the port, and that the vessel was en route to Benghazi.
Hundreds of desperate Libyan civilians had also tried to board but because of the boat's limited capacity, the ramp had to be pulled up for the ship to pull away from the dock in safety.
Before departing, 180 tonnes of humanitarian aid, including food and medical supplies, were offloaded.
IOM staff in Geneva said they could clearly hear the sound of gunfire while they were in touch by satellite phone with their colleagues at the port.
In New York, Moreno-Ocampo told the UN Security Council that the Libyan government had started preparing to counter protests weeks before they started on February 15 -- warned by uprisings in Egypt and Tunisia.
"As early as January, mercenaries were being hired and brought into Libya," he said. "Widespread and systematic attacks against the civilian population have been and continue to be committed in Libya, including murder and persecution, as crimes against humanity."
Saying he had witnesses, videos and photos to back his case, he promised to request "arrest warrants against three individuals who appear to bear the greatest criminal responsibility for crimes against humanity" in Libya.
Diplomats have said Gaddafi is likely to be on the first list of warrants, but Moreno-Ocampo did not name anyone.
The ICC prosecutor said he was also investigating the deaths of dozens of sub-Saharan Africans in the rebel bastion of Benghazi by an "angry mob" who believed they were mercenaries in Gaddafi's pay.
Libyan deputy foreign minister Khaled Kaim dismissed Moreno-Ocampo's findings as biased before they were even revealed on Tuesday, saying: "I'm sure that any decision or any conclusion... will be just a one-party position."
In Washington, State Department spokesman Mark Toner issued an appeal for the Gaddafi regime "to cease hostilities in Misrata port."
Three loud explosions were heard in Tripoli early Wednesday as jets flew overhead, days after Gaddafi narrowly escaped a NATO air strike that killed one of his sons and three grandchildren.
However, Gaddafi was in good health, according to Kaim. In Brussels, NATO military chiefs gathered for a two-day meeting, with French Foreign Minister Alain Juppe saying the aim of the Western alliance's air campaign was to weaken Gaddafi but not to kill him.
Juppe acknowledged the air campaign, now in its seventh week, was taking time, but said "there is no question of getting bogged down in Libya."
