Details added (first version posted at 04:02)
Saif al-Arab Gaddafi, youngest son of Libyan leader Muammar Gaddafi, was killed in NATO's strike against Gaddafi's house, said a spokesman of the Libyan government, Xinhua reported.
The NATO attack against Gaddafi's house resulted in the deaths of Saif al-Arab Gaddafi, 29, youngest son of Gaddafi, and three of Gaddafi's grandchildren, said Mossa Ibrahim, the government spokesman.
The leader himself and his wife, who were in the house, were in good health, while other people injured in the attack, said the spokesman.
This is a direct operation to assassinate the leader, said the spokesman.
The attacks had no legal or political foundations, he said, saying the strike was a violation of the international law.
Asserting he would not leave, embattled Libyan leader Muammar Gaddafi floated on Saturday a proposal for a ceasefire and negotiations in a televised speech.
He said that all parties concerned should follow the truce, and the NATO forces must stop their attacks.
Gaddafi ruled out the possibility that he will quit and leave Libya, which he has been ruling over the past 41 years.
Gaddafi slammed the air raids by NATO, which started to attack his fortified compound in the capital Tripoli.
The world's major powers, the UK, the US and France, started on March 19 to launch strikes from the air and sea against Gaddafi's forces after the UN Security Council passed a resolution to impose a no-fly zone over Libya and authorize "all necessary measures" to protect civilians in Libya