Tripoli, Libya ? Trying to outmaneuver Western military intervention, Moammar Gadhafi’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.

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 Barack 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,” 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.”

In a joint statement to Gadhafi 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 Gadhafi to end his troops’ advance toward Benghazi, the rebel headquarters, 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.

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. 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 Gadhafi’s snipers were on rooftops and his forces were searching homes for rebels.

“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.

Libya’s deputy foreign minister, Khaled Kaim, denied government forces had violated the cease-fire and invited four nations to send observers to monitor compliance: Germany, China, Turkey and Malta.

“The cease-fire for us means no military operations whatsoever, big or small,” he told reporters in Tripoli.

He said military forces were positioned outside Benghazi but that the government had no intention of sending them into the city.

He also invited the U.N. chief to send a fact-finding mission and asserted that the rebels had committed crimes against humanity.

But Susan Rice, the U.S. ambassador to the United Nations, said Gadhafi is violating the U.N. resolution. She told CNN the resolution demanded an immediate cease-fire and end to all offensive operations.