A NATO air strike in the Libyan capital Tripoli killed the youngest son of Qaddafi and three of his grandchildren, Foreign Ministry spokesperson Moussa Ibrahim said in a news conference last night, the New York Times reports. The deaths have not yet been independently confirmed.

Saif al-Arab, 29, and three of Qaddafi's grandchildren, all reported to be under 12, died at their villa in the Bab al-Aziziya compound. The Libyan leader himself and his wife were in the villa at the time, Ibrahim said, but were unharmed.

The airstrike came after NATO rejected a cease-fire offer from Qaddafi yesterday, saying his forces must stop their attacks on civilians before it considers any truce.

Ibrahim said the strike was a “direct operation to assassinate” Qaddafi, and it "is not permitted by international law. It is not permitted by any moral code or principle.” However, Lieutenant-General Charles Bouchard, who commands the alliance’s operation, said in a statement on NATO’s website that "We do not target individuals."

UPDATE: This article previously featured a photograph and reference to Qaddafi's son Saif-al Islam rather than Saif al-Arab.