Libya has declared an immediate ceasefire in the month-long battle against rebels fighting to overthrow strongman Muammar Gaddafi, but the insurgents dismissed it as a bluff and Washington demanded action, not words.
More than four hours after the announcement, rebels said they were still being attacked by Gaddafi loyalists, a claim Tripoli denied.
The rebels also said they were coordinating with Western nations eventual air strikes against Gaddafi's forces, as a coalition of countries geared up to launch attacks after the UN approved action to stop Gaddafi from crushing the insurgency.
Earlier, Foreign Minister Mussa Kussa said "Libya has decided an immediate ceasefire and an immediate halt to all military operations."
The Security Council voted on Thursday to permit "all necessary measures" to establish a no-fly zone, protect civilian areas and impose a ceasefire on Gaddafi's military.
Resolution 1973 "demands the immediate establishment of a ceasefire and a complete end to violence and all attacks against, and abuses of, civilians."
Kussa said Libya, as a member of the United Nations, was "obliged to accept the UN Security Council's resolutions."
But only hours earlier, Gaddafi told Portuguese television the council had "no mandate" for such a resolution, "which we absolutely do not recognise."
Early on Friday evening, rebel military council official Khaled al-Sayeh told a press conference in Benghazi the "Gaddafi regime never stopped firing or attacking people. Until this moment he is still attacking places that are under siege."
He said there was "sustained shelling" in Zintan, Ajdabiya and Misrata.
"There is coordination with the different international bodies for the action to be taken and some places have already been specified," Sayeh of the rebels' military council told reporters in the rebel-held city of Benghazi.
A Libyan military source in Tripoli said the "armed forces are respecting the announced ceasefire and the commitment to protect civilians, and have not carried out any military operations" since the announcement.
Rebel military commander Khalifa Heftir, speaking in the rebels' eastern bastion of Benghazi, accused Gaddafi of "bluffing."
"All the world knows that Muammar Gaddafi is a liar," he said. "He and his sons, and his family, and all those with him are liars."
US Secretary of State Hillary Clinton said reports of a ceasefire would be judged on "action" not words.
"This is a fluid and dynamic situation. We are going to be not responsive or impressed by words. We would have to see actions on the ground," Clinton said, adding that the United States and its allies were still considering what would be "the most effective measures" to end the crisis and repeating calls for Gaddafi to go.
Meanwhile, the White House said US President Barack Obama is to speak on Libya at 1800 GMT Friday. It said the president would meet with key lawmakers in the secure White House Situation Room before making his statement.
EU foreign policy chief Catherine Ashton said, "The issue of course is what's the significance of the statement on the ceasefire and how that fits in."
"Our view is that Gaddafi should go," she reiterated.
Meanwhile, NATO said it was discussing its eventual role in enforcing the resolution, and the Arab League announced a high-level meeting with the European Union and African Union in Paris on Saturday, with UN chief Ban Ki-Moon attending.
So far Belgium, Britain, Canada, France, Italy, Norway, Spain, Sweden, Qatar and the United States have said they will help to implement the no-fly zone.
French government spokesman Francois Baroin said Friday, before the ceasefire announcement, that strikes would come "rapidly... within a few hours."
The aim would be to "protect the Libyan people and to allow them to go all the way in their drive for freedom, which means bringing down the Gaddafi regime," he said.
British Prime Minister David Cameron said London would deploy Tornado and Typhoon warplanes as well as air-to-air refuelling and surveillance aircraft to airbases "from where they can take the necessary action."
Britain has an airbase on the eastern Mediterranean island of Cyprus.
There was no immediate indication of possible targets but a highly-placed French source last week mentioned Gaddafi's Bab al-Azizia command headquarters in Tripoli, a military air base in Sirte, east of the capital, and another in Sebha in the south.
The United Nations has estimated more than 1,000 people have been killed in the uprising.
In The Hague, the prosecutor of the International Criminal Court warned that any indiscriminate attack on civilians in Benghazi would constitute "war crimes."
"The commanders will be responsible. As the prosecutor of the ICC, I will request an arrest warrant against them." Luis Moreno-Ocampo said.
Announcing the ceasefire, Libya's foreign minister said Tripoli was encouraging the "opening of channels of dialogue with all parties," although he did not elaborate.
However, he said he "deeply regretted" the UN resolution, which he said would "aggravate the suffering of the Libyan people."
Benghazi erupted with fireworks and joyful gunfire after news spread of the UN resolution.
Celebrations in Libya's second city lasted through the night, with tracer bullets and anti-aircraft fire ripping through the sky, punctuated by the blaring of car horns.
World oil prices fell in volatile trade after the ceasefire announcement.
Brent North Sea crude for delivery in May dropped $3 before recovering to $114.15 a barrel in London trade, down 75 cents from Thursday.
Meanwhile the UN refugee agency and International Organisation for Migration said that one of the biggest humanitarian evacuations in history would be required to move people from Libya's borders with Tunisia and Egypt.
Some 300,000 people have fled Libya since the rebellion began and many more are expected to leave, the agencies said.
Elsewhere in the Middle East, four protesters were killed by security forces in the Sirian city of Daraa, south of Damascus, and hundreds wounded, a human rights activist contacted by AFP said.
In Yemen, President Ali Abdullah Saleh announced a state of emergency after medics said 41 people were killed when regime loyalists and police opened fire on protesters demanding his ouster in Sanaa.
In Sunni-ruled Bahrain, thousands of Shiites demonstrated after Friday prayers in defiance of martial law and a deadly crackdown by the strategic Gulf kingdom's security forces.
And Saudi King Abdullah warned security forces would "hit" whoever "considers" undermining the kingdom's security and stability, in a televised speech coupled with an announcement of improved social benefits.