Nato strikes have seriously degraded Muammar Gaddafi's military power and his leadership is becoming more isolated, the alliance's secretary-general, Anders Fogh Rasmussen, said on Thursday.

Rasmussen said a combination of strong military and political pressure and opposition support would eventually lead to the collapse of Gaddafi's rule.

'We have significantly degraded Gaddafi's war machine. And now we see results, the opposition has gained ground,' Rasmussen told a news conference.

'We will keep strong military pressure on the Gaddafi regime and I am confident that combination of strong military pressure and increased political pressure and support for the opposition will eventually lead to the collapse of the regime,' he said.

Rasmussen said ending the war required non-military action to complement force.

U.S. and European officials have said Nato has adopted a more aggressive approach to air strikes in Libya after two months of attacks on Gaddafi's government and military failed to make the defiant leader resign.

The Libyan government denied reports on Thursday that Gaddafi's wife, daughter and a top oil official had fled the country to neighbouring Tunisia.

A Nato airstrike on a house in Tripoli is believed to have killed Gaddafi's youngest son and three grandchildren, and there has been speculation about Gaddafi's whereabouts and health since then.

The United Nations has been negotiating with Libya's government, rebels and Nato for a ceasefire of up to three days to allow food and medical supplies to reach civilians, including residents of the city of Misrata, a key battleground. – Reuters