Libyan fighters are so far holding off on attacking one of ousted leader Moammar Gadhafi's last strongholds, as efforts continue to avoid a bloody battle for the city of Bani Walid.

More anti-Gadhafi reinforcements arrived outside the town Monday. They joined thousands of fighters who continue to observe a one-week extension, which expires Saturday, given to all loyalist holdouts to surrender. Provisional authority negotiators have been holding on and off negotiations with tribal elders from the city.

Bani Walid is one of the three remaining pro-Gadhafi bastions. It is dominated by Libya's largest tribe, the Warfalla, which helped anchor Mr. Gadhafi's nearly 42-year rule. However, many of the anti-Gadhafi fighters encircling the town are also Warfalla members.

Libya's interim National Transitional Council has been focused on the city, about 170 kilometers southeast of the capital, Tripoli, because members of Mr. Gadhafi's inner circle were last seen fleeing there.

NTC officials say at least two of the former leader's sons had been in the town in recent days and his spokesman, Moussa Ibrahim, is still believed to be there. They say Seif al-Islam Gadhafi, the former leader's most prominent son, fled Bani Walid for the southern deserts.

Also Monday, officials in Niger, Libya's southern neighbor, said the head of Mr. Gadhafi's security brigades, Mansour Dhao, crossed into the country with several other Libyans whose identities were not released.

A source told the French news agency the group did not include any of Mr. Gadhafi's close relatives or the former leader himself.

NATO said Monday it bombed several targets overnight near Sirte, another Gadhafi stronghold that has not fallen to provisional authority fighters. NATO has carried out airstrikes against pro-Gadhafi forces since March under a U.N. mandate to protect civilians.

Meanwhile, Libya's interim interior minister said about half the country's police force has returned to duty in the capital. Ahmed Darratt and other Libyan officials met with special United Nations envoy Ian Martin in Tripoli Monday to discuss cooperation on human rights and justice issues.

The New York Times reported that Martin also visited the NTC's main Jadida Prison which he said now has 700 inmates, about half sub-Saharan Africans and half Libyans – most accused of supporting the previous government.

Black African migrant workers say they are frequently targeted for arbitrary arrest, accused of having joined Mr. Gadhafi's forces as mercenaries.