The 69-year-old leader, urging civilians to take up arms against rebel "rats," said in an audio broadcast that he was in the city and would be "with you until the end." But there was little sign of popular opposition to the rebel offensive, two of Gaddafi's sons were seized and it was unclear where he was.

World leaders were in no doubt that, after six months of an often meandering revolt backed by NATO air power, the disparate and often fractious rebel alliance was about to take control of the North African desert state and its extensive oil reserves.

"Time has run out," said Franco Frattini, foreign minister of former colonial power Italy, adding that Gaddafi's forces now controlled no more than 10 or 15 percent of the capital.

US President Barack Obama urged Gaddafi to accept defeat as sporadic gunbattles crackled across Tripoli. The European Union, whose members had in recent years resolved disputes with Gaddafi in return for energy supplies, said his time was up.

"We seem to be witnessing the last moments of the Gaddafi regime and call on Gaddafi to step down without further delay and avoid further bloodshed," an EU spokesman said.