Updated at 5:53 p.m. ET
TRIPOLI, Libya - Trying to outmaneuver Western military intervention, Muammar Qaddafi's government declared a cease-fire on Friday against the rebel uprising faltering against his artillery, tanks and warplanes. The opposition said shells rained down well after the announcement and accused the Libyan leader of lying.
At a news conference in Tripoli, foreign minister Moussa Koussa said military operations have been suspended, CBS News correspondent Mark Phillips reports.
Wary of the cease-fire, Britain and France took the lead in plans to enforce a no-fly zone, sending British warplanes to the Mediterranean and announcing a crisis summit in Paris with the U.N. and Arab allies. In Washington, President Obama ruled out the use of American ground troops but warned that the U.S., which has an array of naval and air forces in the region, would join in military action.
There should be no doubt about the Libyan leader's intentions "because he has made them clear," Mr. Obama said. "Just yesterday, speaking of the city of Benghazi, a city of roughly 700,000, he threatened 'we will have no mercy and no pity.' No mercy on his own citizens."
Video: Consequences for Qadaffi?
Arab television station Al-Jazeera reports that a radio station in Benghazi has called on youths to take up arms and prepare for battle, according to CBS News' Khaled Wassef.
In an attempt to prove that the regime had actually stopped its violent campaign against the rebellion, Khaled Kaim, a deputy foreign minister, told reporters that the regime welcomes any nation to send observers to report on the cease-fire. Kaim specifically invited China, Germany, Malta and Turkey to send observers. China and Germany abstained from the U.N. Security Council's vote Thursday evening authorizing the use of military force against Libya.
Kaim continued the regime's policy of not referring to members of the rebellion as civilians or Libyans. He told reporters that no civilians died in military operations, just security force members and those in "armed militias."
U.S. Ambassador Susan Rice said late Friday afternoon that Qaddafi is violating the Security Council's resolution, the Reuters news agency reported.
Earlier, in a joint statement to Qaddafi late Friday, the United States, Britain and France backed by unspecified Arab countries said a cease-fire must begin "immediately" in Libya, the French presidential palace said.
The statement called on Qaddafi to end his troops' advance toward Benghazi and pull them out of the cities of Misrata, Ajdabiya and Zawiya, and called for the restoration of water, electricity and gas services in all areas. It said Libyans must be able to receive humanitarian aid or the "international community will make him suffer the consequences" with military action.
Imposing a U.N.-authorized no-fly zone over Libyan air space will be just a matter of "perhaps hours, perhaps a day or two," CBS News national security correspondent David Martin reports.
Parts of eastern Libya, where the once-confident rebels this week found their hold slipping, erupted into celebration at the passage of the U.N. resolution on Libya. But the timing and consequences of any international military action remained unclear.
Misrata, Libya's third-largest city and the last held by rebels in the west, came under sustained assault well after the cease-fire announcement, according to rebels and a doctor there. The doctor, who spoke on condition of anonymity because he feared reprisals, said Qaddafi's snipers were on rooftops and his forces were searching homes for rebels.
(Below, watch a YouTube video from Misrata Friday)
"The shelling is continuing, and they are using flashlights to perform surgery. We don't have anesthetic to put our patients down," said the doctor, who counted 25 deaths since the morning.
The rebels still hold eastern Libya, which has most of the country's oil reserves. Oil prices slid after the cease-fire announcement, plunging about $2.50 in the first 15 minutes of New York trading. They were down slightly for the week, settling at $101.07 per barrel on the New York Mercantile Exchange.
Mustafa Gheriani, a spokesman for the rebels, said the opposition is considering calling Qaddafi's bluff by holding new protests in Tripoli and elsewhere in Qaddafi's western strongholds to see if his forces open fire.
"The idea is that when he cannot bomb civilians, the whole world will see that Libya does not want him," Gheriani said. "I believe his troops in Tripoli will leave him. We want to make our revolution a peaceful one again, just surround his compound and make him leave."
Gheriani and Khaled Sayh, another rebel spokesman, said shelling continued late Friday in Zintan, a western mountain town; Misrata and Ajdabiya, an eastern city that has been surrounded by government forces.
But even in advanced militaries, orders can take time to make it through the ranks, and it wasn't clear if all of Qaddafi's front-line troops had received the cease-fire directive by late Friday.
In Washington, Secretary of State Hillary Rodham Clinton said the immediate objective of any intervention was to halt violence against civilians, but insisted that the "final result of any negotiation would have to be the decision by Col. Qaddafi to leave." She called on Qaddafi's forces to pull back from eastern Libya.
An administration official said Clinton was essentially doubling down the pressure on Qaddafi, by urging him not only to halt the violence but to start retreating. The official noted that separating the two sides might not actually work: Rebel forces would likely rush into the gaps left by retreating pro-government forces or try to provoke them into harsh retaliation.
The U.N. Security Council resolution, which passed late Thursday, set the stage for airstrikes, a no-fly zone and other military measures short of a ground invasion.
The U.S. was proceeding cautiously in the face of Libya's announcement, as Mr. Obama attempted to navigate between exercising too much U.S. military power and doing too little to help rebels seeking Qaddafi's ouster.
"The driving consideration is what comes next if a no-fly zone doesn't work," said Aaron David Miller, a former Mideast adviser to six U.S. secretaries of state.
"I think Qaddafi's capacity to survive has little or nothing to do with us. If anything, we've lent to his bizarre system of government through the way we've demonized him in the past. To some degree, we've played into his hands," said Miller, now with the Woodrow Wilson Center think tank.
After the resolution passed, a crowd watching the vote on an outdoor TV projection in Benghazi the first city swept up in the uprising that began Feb. 15 burst into cheers, with green and red fireworks exploding overhead. In Tobruk, another eastern city, happy Libyans fired weapons in the air to celebrate.
"We think Qaddafi's forces will not advance against us. Our morale is very high now. I think we have the upper hand," said Col. Salah Osman, a former army officer who defected to the rebel side. He was at a checkpoint near the eastern town of Sultan.
Western powers faced pressure to act quickly as Qaddafi's forces gained momentum.
"We're extremely worried about reprisals by pro-government forces and security agents in Libya. No one knows what's going on in the towns recaptured, and what's going on in prisons and other state security premises across the country," said Rupert Colville, spokesman for the U.N. Office of the High Commissioner for Human Rights. "We are very concerned that the government could resort to collective punishment and we have no illusions about what this regime is capable of."
More than 300,000 people have fled Libya since fighting began, the U.N. said Friday, and the exodus shows no signs of slowing. The U.N. said between 1,500 and 2,400 people have been crossing the borders with Egypt and Tunisia each day.
Melissa Fleming, the spokeswoman for the U.N. refugee agency, said officials were working with Egypt which borders eastern Libya to prepare for a potentially "massive influx of people fleeing the violence in Libya."
"It is also possible that the current conflict could cut off access to safe places and passage out of the country," she said.