Libyan leader Muammar Gaddafi has made it clear that he will not step down, despite the first big protest against him in the capital in months and a UN warning that his government was running out of food.

Gaddafi is emphatic he will not leave Libya, South African President Jacob Zuma said after talks with the Libyan leader, dashing prospects for a negotiated end to the conflict.

Zuma was in Tripoli yesterday to try to revive an African 'roadmap' for ending the conflict, which started in February with an uprising against Gaddafi and has since turned into a war with thousands of people killed.

Libyan rebels and NATO have set Gaddafi's departure as the main condition for any ceasefire. With Gaddafi's refusal to leave, the talks with Zuma produced no breakthrough.

But new questions emerged over how long Gaddafi could hold on after a senior United Nations aid official said shortages of food and medicine in areas of Libya controlled by Gaddafi amounted to a 'time bomb.'

Panos Moumtzis, the UN humanitarian coordinator for Libya, told Reuters in Tripoli that some food stocks in areas under Gaddafi's control were likely to last only weeks.

Protests in Tripoli

In another development that cast doubt on Gaddafi's assertions that he is in control, witnesses in the Souq al-Juma suburb of Tripoli said a large anti-government protest took place there on Monday. Their accounts lent weight to rebel claims that opposition to Gaddafi was stirring in the capital.

The protest, apparently the biggest confirmed protest inside Tripoli since Western forces began bombing the country in March, was broken up by security forces firing weapons, residents said.

Asked about the incident at a news conference government spokesman Moussa Ibrahim said: 'I have heard of the event. I did not have enough time to get information.'

Meanwhile, Moussa Ibrahim claimed today that NATO's bombing campaign has killed 718 Libyan civilians.

He said 4,067 civilians had been wounded, 433 of them seriously. the figures were current to 26 May.

He said these figures did not include Libyan military casualties, a toll the defence ministry refuses to divulge.

NATO has denied killing large numbers of civilians, and foreign reporters in Tripoli have not been shown evidence of large numbers of civilian casualties.

Asked why the authorities had not shown large numbers of casualties to foreign media, Ibrahim said this was because the casualties had not been concentrated near Tripoli but scattered across the country.

Ibrahim described the departure of Gaddafi as a ‘worst case scenario’ for the country.

He said Gaddafi did not discuss ‘exit strategies’ with Mr Zuma on his visit to Libya yesterday.

Mr Zuma ‘never discussed any exit strategies as they have been described in the media,’ he said.