"Time is on our side, time is not on the side of Colonel Kadhafi who's losing his leading military commanders," Cameron told reporters in Prague.
"The sands of time are running out for him, and so we need to be patient and persistent," he added.
International Criminal Court judges will on Monday decide whether to issue an arrest warrant for Kadhafi for crimes against humanity, the court said on its website on Thursday.
"We will resist and the battle will continue to the beyond, until you're wiped out. But we will not be finished," Kadhafi said in an audio message on Libyan television late on Wednesday.
"There's no longer any agreement after you killed our children and our grandchildren... We have our backs to the wall. You (the West) can move back," Kadhafi said in homage to his comrade Khuwildi Hemidi, several members of whose family were killed on Monday in reported NATO raids on his residence.
NATO has acknowledged its warplanes early on Monday hit Sorman west of Tripoli but insisted that the target was military.
Libyan government spokesman Mussa Ibrahim said 15 people, including three children, were killed in what he called a "cowardly terrorist act which cannot be justified."
Rebel colonel Ahmed Omar Bani on Thursday made a plea for foreign allies to provide the arms, training and communications systems needed to defeat Kadhafi.
"It is so urgent" he said, "we will fight, just support us, just give us the equipment."
Much of the rebels' arsenal comprises Soviet-era tanks and artillery up to 50 years old.
NATO on Wednesday pledged to carry on bombing military targets in Libya, saying more civilians would die if operations were not maintained under a UN mandate to protect Libyans from the exactions of Kadhafi's regime.
"NATO will continue this mission because if we stop, countless more civilians could lose their lives," NATO chief Anders Fogh Rasmussen said in a video statement on the alliance's website.
He did not directly refer to Italy, whose Foreign Minister Franco Frattini on Wednesday called for "an immediate humanitarian suspension of hostilities" in Libya.
"We have seen the effects of the crisis and therefore also of NATO action not only in eastern and southwestern regions but also in Tripoli," Frattini told a parliamentary committee in Rome.
"I believe an immediate humanitarian suspension of hostilities is required in order to create effective humanitarian corridors," while negotiations should also continue on a more formal ceasefire and peace talks, he said.
The commander of the NATO operation, Canada's Lieutenant General Charles Bouchard, said a ceasefire risked becoming "just an opportunity for both sides to reload and to engage in further violence down the road."
"We must continue to stay engaged to prevent that rearming," Bouchard said.
Frattini's comments had drawn a swift rebuff from NATO ally France which has played a leading role in the military intervention in Libya.
The rebels also dismissed the Italian proposal.
"Even if NATO halts operations, we will fight tooth and nail, we will fight until our country is freed, we don't fear (a NATO cessation)," rebel spokesman Mahmud Shamam said.
Shamam also told French daily Le Figaro the rebels were in indirect contact with the regime and may be prepared to allow Kadhafi to stay in Libya, but that he and his family must agree to leave power.
"Our conditions remain the same. It is totally excluded that Kadhafi or members of his family take part in a future government. We are discussing with them the mechanism for Kadhafi's departure," he said.
In Benghazi, however, National Transitional Council deputy chairman Abdel Hafiz Ghoga told AFP: "There is no contact, direct or indirect, with the Kadhafi regime."
Meanwhile, a ship carrying 49 people fleeing the conflict arrived at the Tunisian port of El Ketef, including 19 defecting police and soldiers, the TAP news agency said.
The developed countries took the near unprecedented step on Thursday of drawing down their oil reserves to make good the loss of Libyan supply, aiming to keep prices in check.
The United States took the lead, saying it would release 30 million barrels from its stocks, which at 727 million barrels were at a historic high.
The International Energy Agency said, meanwhile, that 60 million barrels would be taken from reserves over the next month to cover lost Libyan output, only the third time the 28-member group has taken such a step.
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