Nato air strike in the Libyan capital, Tripoli, has killed the son of the Libyan leader, Colonel Gaddafi,

a government spokesman has said.

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

His son Saif al-Arab was killed, as well as three of his grandsons.

Journalists say the building was extensively damaged and one unexploded bomb remains at the site.

Saif al-Arab was the youngest of Col Gaddafi's sons, with a lower profile than his brother Saif al-Islam.

He had been studying in Germany and returned to Libya recently.

Government spokesman Moussa Ibrahim said the villa was attacked "with full power."

"The attack resulted in the martyrdom of brother Saif al-Arab Gaddafi, 29 years old, and three of the leader's grandchildren," he said.

"The leader with his wife was there in the house with other friends and relatives, the leader himself is in good health, he wasn't harmed."

"This was a direct operation to assassinate the leader of this country," the spokesman added.