UN chief Ban Ki-moon said that Libyan leader Muammar Gaddafi has "lost all legitimacy" and must step down, in an interview published on Saturday.
"Gaddafi has lost all legitimacy. He cannot stay in power in Libya. Whatever happens, he has to go," he told the Spanish daily El Mundo.
The UN Security Council on late Thursday passed a resolution approving "all necessary measures" to impose a no-fly zone in Libya, protect civilian areas and pressure Gaddafi into accepting a ceasefire.
The Libyan government on Friday announced an immediate halt to military operations following the resolution.
But the commander of the rebels fighting to overthrow Gaddafi dismissed any ceasefire offer as a bluff.
Ban told El Mundo he was "confused" about the ceasefire "because reports tell us that bombardments are continuing in the outskirts of Benghazi."
"We need to monitor and verify the seriousness of this (ceasefire) statement. That's what we are going to discuss today in Paris with leaders from around from the world," he said in the interview, published in Spanish.
US, European and Arab leaders on Saturday held a Libya crisis summit in Paris with the threat of military strikes against Gaddafi's forces growing ever more intense.
Fighting raged around Libya's rebel stronghold of Benghazi on Saturday as Gaddafi gave a defiant response to the world leaders planning military action against him.
Ban said "world leaders have united and have spoken with one voice" in the UN resolution.
"I have been urging the Libyan authorities to end hostilities immediately, to disarm and to discuss a peaceful transition. That is what the international community expects of Mr Gaddafi and his government."
The international community "cannot tolerate the leader of any government using force against his people."
"From now when people ask for freedom, the leaders will have to listen more carefully," he said.
Ban was in Madrid on Friday to meet with Spanish Prime Minister Jose Luis Rodriguez Zapatero.
In a joint news conference on Friday with Zapatero, he warned the Libyan regime that anyone responsible for attacks on unarmed civilians would be "brought to justice."