A French official says Mirage and Rafale fighter jets are flying over the Libyan city of Benghazi and could strike Libyan tanks.
The official says the jets are flying over the opposition stronghold and its surroundings to ensure that Moammar Gadhafi's forces could not take any action there.
The official says the French operation could strike Libyan tanks later Saturday.
The official spoke on condition of anonymity because of the sensitivity of the operation.
He spoke right after top officials from the United States, Europe and the Arab world announced immediate military action to protect civilians as Gadhafi's forces attacked Benghazi.
Top officials from the United States, Europe and the Arab world have launched immediate military action to protect civilians as Libyan leader Moammar Gadhafi's forces attacked the heart of the country's rebel uprising.
French President Nicolas Sarkozy said after an emergency summit in Paris on Saturday that French warplanes are 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.
"Our planes are blocking the air attacks on the city" of Benghazi, he said, without elaborating. French planes have been readying for an attack in recent days.
Earlier Saturday, Libyan government troops forces stormed into the rebel capital of Benghazi, apparently ignoring a proclaimed cease-fire and potentially complicating any allied military action.
British Prime Minister David Cameron said after the summit: "The time for action has come, it needs to be urgent."
France, Britain and the United States had warned Gadhafi Friday that they would resort to military means if he ignored the U.N. resolution.
U.S. Secretary of State Hillary Clinton was also at Saturday's summit.
A communique from the summit participants, referring to the U.N. Security Council resolution, said: "Our commitment is for the long term: we will not let Colonel Gadhafi and his regime go on defying the will of the international community and scorning that of his people.
"We will continue our aid to the Libyans so that they can rebuild their country, fully respecting Libya's sovereignty and territorial integrity."