BENGHAZI, Libya?(UPDATE) Moammar Gadhafi warned international forces they would "regret" intervening in Libya and his troops attacked the heart of the five-week-old uprising on Saturday, swarming the first city seized by the rebels with shells, gunfire and warplanes.

"Where is France, where is NATO?" cried a 50-year-old woman in Benghazi. "It's too late."

Leaders from the Arab world, Africa, the United States and other Western powers were holding urgent talks in Paris on Saturday over possible military action after the Libyan government, apparently hoping to outflank the effort, declared a ceasefire.

On Saturday, a warplane was shot down over the outskirts of the key rebel-held city 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 in the distance.

Before the plane went down, journalists could hear 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.

The fighting galvanized the people of Benghazi, with young men collecting bottles to make gasoline bombs. Some residents dragged bed frames and metal scraps into the streets to make roadblocks.

At a news conference in the capital, Tripoli, the government spokesman read letters from Gadhafi to President Barack Obama as well as others involved in the international effort.

"Libya is not yours. Libya is for the Libyans. The Security Council resolution is invalid," he said in the letter to French President Nicolas Sarkozy, British Prime Minister David Cameron, and UN Secretary-General Ban Ki-Moon. "You will regret it if you dare to intervene in our country."

To Obama, the Libyan leader was slightly more conciliatory: "If you had found them taking over American cities with armed force, tell me what you would do."

Government spokesman Ibrahim Musa said the rebels are the ones breaking the ceasefire by attacking military forces.

"Our armed forces continue to retreat and hide, but the rebels keep shelling us and provoking us," Musa told The Associated Press.

In a joint statement to Gadhafi late Friday, the United States, Britain and France?backed by unspecified Arab countries?called on Gadhafi to end his troops' advance toward Benghazi and pull them out of the cities of Misrata, Ajdabiya and Zawiya. It also 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 Friday morning.

Libya's deputy foreign minister, Khaled Kaim, denied late Friday that government forces had violated the ceasefire and invited four nations to send observers to monitor compliance: Germany, China, Turkey and Malta.

"The ceasefire 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.