French fighter jets soared over a rebel-held city besieged by Moammar Gadhafi's troops on Saturday, the first mission for an international military force launched in support of the 5-week-old uprising.

French President Nicolas Sarkozy said after an emergency summit in Paris that French jets were already targeting Gadhafi's forces. The 22 participants in Saturday's summit "agreed to put in place all the means necessary, in particular military" to make Gadhafi respect a U.N. Security Council resolution Thursday demanding a cease-fire, Sarkozy said.

Gadhafi had tried to take advantage of the time lag betwen the U.N. resolution and the launch of the international operation, making a decisive strike on the Benghazi, Libya's second-largest city and the first major stronghold of the rebellion. Crashing shells shook buildings, and the sounds of battle drew closer to the city center as its residents despaired. A doctor said 27 bodies had reached hospitals by midday. By late in the day, warplanes could be heard overhead and the shelling had stopped.

"Our planes are blocking the air attacks on the city" of Benghazi, he said, without elaborating. After the announcement, scattered cheers went up from rebels in the city.

In an open letter, Gadafhi warned: "You will regret it if you dare to intervene in our country."

Libyan state television showed Gadhafi supporters converging on the international airport and a military garrison in Tripoli, and the airport in Gadhafi's hometown of Sirte, in an apparent attempt to deter bombing.

Earlier Saturday, a plane was shot down over the outskirts of Benghazi, sending up a massive black cloud of smoke. An Associated Press reporter saw the plane go down in flames and heard the sound of artillery and crackling gunfire.

Before the plane went down, journalists heard what appeared to be airstrikes from it. Rebels cheered and celebrated at the crash, though the government denied a plane had gone down — or that any towns were shelled on Saturday.