Colonel Gaddafi himself was in the large residential villa which was hit by the strike, the spokesman added, but was unharmed.

His son Saif al-Arab was said to be dead, as well as three grandchildren. Nato has confirmed the air strike, without denying or confirming the reported deaths.

A Nato spokesman said the strike had hit a "known command and control building in the Bab al-Azizya neighbourhood".

Lieutenant-General Charles Bouchard said that he was aware of reports that members of Col Gaddafi's family had been killed, but made no further comment.

"We regret all loss of life, especially the innocent civilians being harmed as a result of the ongoing conflict," said Lieutenant-General Charles Bouchard.

The strike that Libya said had killed Saif al-Arab Gaddafi came less than a day after a speech by his father was broadcast on state TV, in which Col Gaddafi called for a ceasefire and negotiations.

Several air strikes against Col Gaddafi's sprawling Bab al-Aziziya compound have been reported recently.