Libyan leader Muammar Gaddafi signalled his defiance in the face of a mounting revolt against his 41-year rule on Tuesday, making a brief appearance on state television and denying he had fled the country.

His forces have cracked down fiercely on anti-government demonstrators, with fighting now spreading to the capital Tripoli after erupting in Libya''s oil-producing east last week.

In his first appearance on television since the revolt broke out, Gaddafi was shown holding an umbrella in a 22-second statement. He denied reports that he had fled to Venezuela, ruled by his friend President Hugo Chavez.

"I want to show that I''m in Tripoli and not in Venezuela. Do not believe the channels belonging to stray dogs," said Gaddafi, leaning out of a van. "I wanted to say something to the youths at Green Square (in Tripoli) and stay up late with them but it started raining. Thank God, it''s a good thing," added Gaddafi, who took power in a military coup in 1969 when he toppled King Idriss.

World powers have condemned the use of force against protesters, with U.N. Secretary General Ban Ki-moon accusing Libya of firing on civilians "from warplanes and helicopters". "This must stop immediately," Ban said. The Security Council was to hold a meeting on Libya later in the day, diplomats said.

Security forces have killed dozens of protesters across the vast, thinly populated nation stretching from the Mediterranean deep into the Sahara desert, rights groups and witnesses said.

As the fighting intensified, cracks were beginning to appear among Gaddafi''s supporters, with some of its ambassadors resigning and siding with the protesters. A group of army officers called on soldiers separately to "join the people".

Demonstrations spread to Tripoli after several cities in the east -- including Benghazi where the protests had first erupted -- appeared to fall to the opposition, according to residents.

Tripoli, a Mediterranean coastal city, appeared calm in the early hours of Tuesday. "There is heavy rain at the moment, so people are at home," one resident said. "I am in the east of the city and have not heard clashes."