Muammar Gaddafi's wife and three of their children entered Algeria on Monday morning, Algeria's Foreign Ministry said, drawing criticism from Libya's rebels who said sheltering the family was an "act of aggression".
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.
A spokesman for the National Transitional Council (NTC) said it considered Algeria's sheltering of the Gaddafi family members an act of aggression and said 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.
Libyan rebel officials had previously accused Algeria -- the only one of Libya's North African neighbours yet to recognise 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 neighbours.
Medelci met Mahmoud Jibril, head of the NTC's executive committee, on the sidelines of an Arab League meeting in Cairo.
Last week, Gaddafi's forces helped his son Mohammed 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.
© 2014 Thomson/Reuters. All rights reserved.