TRIPOLI: Waves of NATO aircraft hit Tripoli Tuesday in the most sustained bombardment of the Libyan capital since Western forces began airstrikes in March. By Tuesday afternoon, war planes were striking different parts of the city several times an hour, hour after hour, rattling windows and sending clouds of grey smoke into the sky. But Muammar Gaddafi vowed to fight to the death as US President Barack Obama said it was only a matter of time until the Libyan leader goes. The Libyan government attributed earlier blasts to NATO airstrikes on military compounds in the capital. At least 29 people were killed in 60 strikes on the Libyan capital Tuesday, government spokesman Moussa Ibrahim told reporters. His account could not be independently verified. “We only have one choice: we will stay in our land dead or alive,” Gaddafi said in a fiery audio address, adding that his supporters were flocking to his vast Bab Al-Aziziya compound, which was hit several times by NATO airstrikes. Describing planes flying overhead and explosions around him, Gaddafi was defiant. “We are stronger than your missiles, stronger than your planes, and the voice of the Libyan people is louder than explosions,” he said in his customary impassioned tone. He said he was ready to unleash between 250,000 to 500,00 Libyans to swarm across the country to cleanse it from “armed gangs”, a reference to rebels controlling eastern Libya. Gaddafi was last seen on state television on May 30. Obama said there had been “significant” progress in the NATO operation. “What you are seeing across the country is an inexorable trend of the regime forces being pushed back, being incapacitated,” Obama said in a news conference in Washington. “I think it is just a matter of time before Gaddafi goes.” Contact with rebels World powers were making diplomatic overtures to the rebels, including Russia and China, despite misgivings about interference in Libya's sovereign affairs. Mikhail Margelov, Special Representative for the President of Russia for Africa, told reporters in the rebel capital of Benghazi that Gaddafi can no longer represent Libya. “We highly believe that Gaddafi has lost his legitimacy after the first bullet shot against the Libyan people,” he said. In Beijing, the Chinese Foreign Ministry said an Egypt-based Chinese diplomat had visited Benghazi for talks with the rebel-led National Transitional Council. China has declined to take sides, but its moves reflect recognition that Gaddafi's days may be numbered, said Yin Gang, an Arab expert at the Chinese Academy of Social Sciences.