Toppled Libyan leader's wife, his daughter and two of his sons in Algiers, as NTC says it will seek their extradition.
File picture of Muammar Gaddafi's wife Safia, left, daughter Aisha, centre, and son Hannibal [Reuters]
Muammar Gaddafi's second wife, two of his sons and his daughter have entered Algeria, according to the Algerian foreign ministry.
"The wife of Muammar Gaddafi, Safia, his daughter Aisha, and sons Hannibal and Mohammed, accompanied by their children, entered Algeria at 08:45am local time [0745GMT] through the Algeria-Libyan border," the ministry said in a statement on Monday published by the APS news agency.
However, it gave no information on the toppled Libyan leader, whose whereabouts has remained a mystery since fighters opposed to his government seized control of Tripoli, the Libyan capital, last week.
Algeria said their arrival had been reported to the United Nations and to the head of Libya's Transitional National Council [NTC], now widely recognised internationally as the country's legitimate government.
The Libyan rebel leadership said on Monday that Algeria had given them "a pass" to enter a third country.
"Algeria said they gave a pass to go to a third country," Mahmud Shammam, a spokesman for the National Transitional Council (NTC), said.
"We cannot confirm that but they said they welcome them [to Algeria] for humanitarian reasons."
Shammam said the rebel leadership did not understand how anyone could "save Gaddafi's family" and wanted them back in Libya.
"Saving Gaddafi's family is not an act we welcome and understand. We'd like those persons to come back," he told a news conference.
"We can assure our neighbours that we want better relations with them ... but we are determined to arrest and try the Gaddafi family and Gaddafi himself."
Shammam said the rebels guaranteed a "fair trial".
Act of aggression
Gaddafi's Sons: Where Are They?
Mohammad: He has entered Algeria. He was captured by Libyan fighters in Tripoli but managed to escape
Hannibal: He is now in Algeria
Saif al-Islam:Believed to have moved to the town of Bin Walid, south of Tripoli
Saif al-Arab:Killed by a NATO air strike in April
Khamis: There are rumours of his death but it has yet to be confirmed
Saadi: At large
Mutasim: At large.
Another NTC spokesman accused Algeria of an act of aggression and also said the council would seek the extradition of Gaddafi's family members.
Ahmed Bani, a military spokesman for the council, said he was unsurprised to hear Algeria had welcomed Gaddafi relatives.
Throughout the six-month Libyan uprising, rebels have accused Algeria of providing Gaddafi with mercenaries to curb the revolution.
Al Jazeera's Anita McNaught, reporting from Tripoli, said: "There have been rumours over the last few days that family members had gone and that Gaddafi himself may have gone.
"The Algerian government has always got on really well with the Gaddafi regime. Algeria is one of the few countries that has not yet recognised the NTC."
Earlier, the Egyptian news agency MENA, quoting unidentified rebel fighters, had reported that six armoured Mercedes cars, possibly carrying Gaddafi's sons or other top regime figures, had crossed the border at the southwestern Libyan town of Ghadamis into Algeria.
Algeria's foreign ministry had denied that report.
Watch: A brief look at Gaddafi's family members
ICC warrant against Khamis?
Meanwhile, Khamis Gaddafi, another of Gaddafi's sons, whose military unit is accused of killing dozens of detainees in Tripoli, may be placed on the international war crimes court's most-wanted list, the prosecutor told the Reuters news agency on Monday.
The Hague-based International Criminal Court [ICC] has already approved warrants for the arrest of Gaddafi, his son Saif al-Islam, and Libyan intelligence chief Abdullah al-Senussi on charges of crimes against humanity.
Luis Moreno-Ocampo, the ICC prosecutor, said he may also apply for an arrest warrant for Khamis, after Human Rights Watch said members of the Khamis Brigade, a force commanded by him, appeared to have carried out summary executions of detainees whose bodies were found in a warehouse in Tripoli.
"We know Khamis should also be prosecuted because he was the commander of the brigade that was more active on some of the crimes," Moreno-Ocampo said.
Moreno-Ocampo said a UN Human Rights Council commission would conduct further investigations on the ground in Libya soon and that he would base his decisions on the results.