Last Updated 9:58 a.m. ET
BENGHAZI, Libya Libyan leader Muammar Qaddafi appeared to defy the United Nations' call for an end to violence and even his own government's claim of an immediate cease-fire, with continued strikes against rebel forces in Benghazi.
A warplane was shot down over this eastern Libyan rebel stronghold Saturday, though it is unclear whether the jet belonged to Qaddafi's forces or to the rebels.
An Associated Press reporter saw a plane go down in flames outside Benghazi early Saturday, sending up a black cloud of smoke after the city came under attack. The sound of artillery and crackling gunfire was heard in the distance.
Libyan television broadcast live pictures this morning of a pro-Qaddafi demonstration at a Sabha airport. The video, which was taken on an airport runway, appeared to demonstrate the use of human shields.
Arab media has speculated that if Qaddafi's power base in Tripoli is threatened, he may flee to Sabha.
The latest developments come as leaders from the Arab world, Africa, the United States and other Western powers hold urgent talks in Paris Saturday over possible military action against Qaddafi's forces.
Trying to outmaneuver Western military intervention, Qaddafi's government declared a cease-fire on Friday as the rebel uprising faltered against his artillery, tanks and warplanes. But the opposition said shells rained down well after the announcement and accused the Libyan leader of lying.
On Saturday, government spokesman Ibrahim Musa denied that a government plane had gone down. He also denied government forces shelled any Libyan towns on Saturday, saying the rebels are the ones breaking the cease fire by attacking military forces.
CBS News correspondent Mandy Clarke reported on "The Early Show on Saturday Morning" that there is confusion over whose plane it was -- whether it was from government forces or those of the rebels.
Later, Qaddafi said the U.N. resolution authorizing international military intervention in Libya is "invalid.'' The Libyan leader said he sent a message to President Obama defending his decision to attack rebel cities: "If you found them taking over American cities by the force of arms, tell me what you would do?''
The statement came from a government spokesman at a news conference in Tripoli.
Qaddafi also sent a letter to the French and British leaders, and the U.N. secretary general, saying the resolution violates the U.N. charter and saying they would "regret'' any intervention. "Libya is not for you, Libya is for the Libyans,'' he said."
"Our armed forces continue to retreat and hide, but the rebels keep shelling us and provoking us," Musa told The Associated Press.
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 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, 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 Qaddafi'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 late Friday that 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.