Gaddafi wife and three children in Algeria

Their arrival, a week after Tripoli fell into rebel hands, was reported to the United Nations and the Libyan rebel authorities, the state Algeria Press Service (APS) reported, citing a statement from the ministry.

"Muammar Gaddafi's wife Safia, his daughter Aisha, his sons Hannibal and Mohammed, accompanied by their children, entered Algeria at 08.45 a.m. (0745 GMT) through the Algerian-Libyan border," said APS.

Gaddafi's whereabouts remain unknown after Tripoli fell to his foes. The rebels have offered a $1.3 million reward and amnesty from prosecution for anyone who kills or captures him.

Gaddafi's son Khamis, who led the elite and widely feared Khamis brigade, was killed in a clash near the capital, a senior rebel officer said on Monday. No independent confirmation of the death was available.

ACT OF AGGRESSION

A spokesman for the National Transitional Council (NTC) said it considered Algeria's move granting refuge to the Gaddafi family members an act of aggression and it will seek their extradition.

"We have promised to provide a just trial to all those criminals and therefore we consider this an act of aggression," spokesman Mahmoud Shamman told Reuters. "We are warning anybody not to shelter Gaddafi and his sons. We are going after them in any place to find them and arrest them," he said.

NTC vice chairman Abdel Hafiz Ghoga echoed this: "All Gaddafi's family are wanted for financial crimes against Libya. His wife, daughter, all of them."

Libyan rebel officials had previously accused Algeria -- the only one of Libya's North African neighbors yet to recognize the NTC -- of backing Gaddafi, an allegation Algeria has denied.

Algerian Foreign Minister Mourad Medelci had held talks with a senior Libyan rebel official, APS reported earlier on Monday, the highest-level contact in months of fraught relations between Libya's new leadership and their Algerian neighbors.

Medelci met Mahmoud Jibril, head of the NTC's executive committee, on the sidelines of an Arab League meeting in Cairo.

Mohammed is the son from Gaddafi's first marriage. Last week, Gaddafi's forces helped him flee house arrest after he was captured by rebels. The loyalist fighters stormed the house where Mohammed was held and set him free after clashes with guards there, Al Jazeera news channel said.

Since the revolt began in February, Aisha Gaddafi has made several public appearances backing her father and attacking the rebels and Western powers trying to overthrow him. Hannibal Gaddafi has kept a low profile since the unrest began.

(Additional reporting by Richard Valdmanis in Tunis, Samia Nakhoul in Tripoli and Robert Birsel in Benghazi)