The Obama administration on Tuesday urged Libya’s neighbors to arrest fleeing members of Moammar Gaddafi’s ousted government, as at least a dozen senior Libyan military officials arrived in Niger after escaping across the southern desert.

U.S. overhead surveillance observed a convoy entering Niger on Tuesday morning, but U.S. and NATO officials said any attempt to stop the vehicles would have been outside their mandate. The State Department and Libyan rebel officials said there was no indication that Gaddafi was among those who fled.

Conflicting reports from rebel forces placed Gaddafi in various locations throughout his tribal heartland, a triangle between his coastal home town, Sirte; the oasis town of Bani Walid to the west, where Gaddafi’s son Saif al-Islam is believed to be hiding; and the city of Sabha, on the edge of the Sahara in the south.

NATO aircraft continued flying strike missions over coastal areas, but officials said that a decreasing number of targets fall within the alliance’s authorized mission of protecting civilians from government forces. That mission has been broadly interpreted to include any massed group of government troops and command-and-control facilities.

The current NATO mandate runs out on Sept. 27; its renewal would require a political decision by alliance members. Military mission commanders could also recommend an end to the bombing before then.

“The actual operational plan says that the end state is whenever we decide we’ve achieved what we set out to do,” said a NATO official, who spoke on the condition of anonymity because he was not authorized to discuss the issue. In Sirte and Bani Walid, Gaddafi “still has organized military forces capable of inflicting damages on civilians. As long as air power is still capable of dealing with that threat, we still have a mission. We’re still destroying stuff every day.”

Although U.S. “national technical means” — satellites and high-flying reconnaissance aircraft — observed the convoy entering Niger, the area is nearly 1,000 miles south of where NATO strike aircraft are operating, the official said. Hitting such targets “would be a completely different operation. . . . We would have to refuel over Libyan territory.”

In addition, he said, the alliance has “no independent means to verify” who is traveling in closed vehicles. “We have no idea where [Gaddafi] is,” the official said. “We really haven’t had a good sense for a while.”

NATO spokesman Col. Roland Lavoie, in Naples, said it is not within the alliance’s mission “to track and target thousands of fleeing former regime leaders, mercenaries, military commanders and internally displaced people.”

Estimates of the number of vehicles in the convoy to Niger varied from 50 to more than 200. An official for the rebels’ governing Transitional National Council said the vehicles were armed and carried more than 250 people. The official, who spoke on the condition of anonymity so he could talk frankly, said the rebels are worried about security along Libya’s thousands of miles of border because they have no ability to lock it down.

Mustafa Abdel Jalil, the head of the council, has asked Niger to stop Gaddafi and his top officials from crossing the border. But according to council members and media accounts from Niamey, the capital of Niger, the loyalist convoy was welcomed inside the country.

State Department spokeswoman Victoria Nuland said that, based on U.S. conversations with Nigerien officials, those arriving in the convoy appeared to include “some dozen or more senior members of the regime” and “members of the senior military staff.” All of them, she said, were subject to a U.N. travel ban on members of the Gaddafi government, and some may be under indictment by the International Criminal Court.

“We have strongly urged the Nigerien officials to detain those members of the regime who may be subject to prosecution, to ensure that they confiscate any weapons that are found and to ensure that any state property of the government of Libya — money, jewels, et cetera — also be impounded so that it can be returned to the Libyan people.”

“Our understanding is that they are going to take appropriate measures,” Nuland said, and work with the rebel council in Libya “on what is to be done with both the people and the property.”

Nuland said the administration has made similar overtures to “all of the neighboring states . . . about their U.N. Security Council obligations, and those conversations will continue.” Gaddafi’s second wife, his daughter and son, and numerous other family members fled last week to Algeria, whose government has said they were admitted for “humanitarian reasons.”

Burkina Faso, like Niger a recipient of Libyan aid over the years, has said it will grant asylum to Gaddafi and members of his family. On Tuesday, however, the Foreign Ministry in Ouagadougou, the capital, said it had received no request for exile from Gaddafi and he was not expected there. Burkina Faso has recognized the Transitional National Council as Libya’s official government.

The convoy crossed the border as negotiations broke down over Bani Walid, where the rebels have given a one-week extension to loyalist forces to surrender or face attack. Late Tuesday, however, an al-Jazeera correspondent outside the town reported that talks had collapsed, rebel negotiators had been fired upon and an attack was imminent.

As the hunt for Gaddafi continued, his die-hard supporters remained defiant Tuesday. “We are fighting and resisting for the sake of Libya and all Arabs,” Moussa Ibrahim, Gaddafi’s spokesman and the public face of his government, told the Syria-based al-Rai television station, a pro-Gaddafi channel. “We are still strong and capable of turning the tables on NATO.”

To counter reports that Gaddafi was planning to flee, Ibrahim told al-Rai that the longtime ruler was in “excellent health, planning and organizing for the defense of Libya.”

After he spoke, a video was posted on rebel Facebook pages of fighters who have detained Gaddafi’s deputy foreign minister, Khaled Kaim. The video showed Kaim sitting on a bed, being interrogated by rebels who called him a “liar” and a “dog” and accused him of using foreign mercenaries against them.

Fadel reported from Tripoli.