By CNN Wire Staff, and CNN's Barbara Starr and Matthew Chance
Embattled Libyan leader Moammar Gadhafi may be making preparations for what is described as a "last stand" in Tripoli as a months-long NATO air campaign continues amid reports of rebel advances, according to two U.S. officials.
"We believe he could be planning for a last stand," one U.S. official said.
A second U.S. official confirmed a similar concern and said the Gadhafi plan could involve a final military offensive against civilians, launched from his last major strongholds around the Libyan capital.
The officials, who have knowledge of the situation on the ground, did not want to be named because of the sensitive intelligence matters.
In an address broadcast on state television Monday, Gadhafi urged supporters to take up arms and battle rebel forces.
"Move always forward to the challenge; pick up your weapons; go to the fight in order to liberate Libya inch by inch from the traitors and from NATO. Be prepared to fight if they hit the ground," Gadhafi said.
Both officials emphasized that if a final push by Gadhafi happens, the United States doesn't have a clear idea what form it could take.
Officials say they have no indication Gadhafi is making preparations to leave the country.
However, State Department spokesman Mark Toner said Friday that U.S. officials in Benghazi have been working with the Libyan opposition "on exactly what it's going to look like post-Gadhafi."
"Impossible to say when he'll go, but it's clear that he will go," Toner told CNN's Brooke Baldwin.
Libyan Prime Minister al-Baghdadi al-Mahmoudi said Thursday that neither Gadhafi nor his relatives would leave the country.
The speculation over a Gadhafi "last stand" comes as his government's troops are battling rebel forces on a number of fronts, including in the west, where fighting has raged for days over the strategic city of Zawiya, about 30 miles west of Tripoli.
Fierce artillery fire could be heard around Zawiya on Friday. Rebels took a major oil refinery there, said Hobab Jomaa, a rebel fighter. They were in control of the western part of the city, but battles continued in the eastern part, he said.
The International Organization for Migration said Friday that it is working to evacuate an unknown number of foreign nationals from Tripoli and other western cities "who are increasingly vulnerable and now want to leave."
Meanwhile, a NATO airstrike destroyed the home of Abdullah al-Sanussi, the head of Libya's intelligence service and a brother-in-law of Gadhafi's, neighbors and Libyan government officials said Friday.
The strike also destroyed a school and medical store, neighbors and officials said. One person - not al-Sanussi - was killed, they said.
In June, the International Criminal Court issued an arrest warrant for al-Sanussi along with Gadhafi and his son Saif al-Islam for actions taken as a popular uprising morphed into civil war.
The warrants are for "crimes against humanity," including murder and persecution committed in Libya in February "through the state apparatus and security forces."
Gadhafi's government has rejected the court's authority.
"This court is nothing but a cover to the military operations of NATO," Libyan Justice Minister Mohammed Al Qamod has said. "It is merely a political tool for exerting pressure and political blackmail against sovereign countries."
The attack on al-Sanussi's house followed a NATO airstrike Thursday night that killed a brother of Moussa Ibrahim, the spokesman for the government in Tripoli, a Libyan government official said.
Hasan Ali Ibrahim, a younger brother of Moussa Ibrahim, was working as a civilian volunteer for the Gadhafi government, the official said. The 25-year-old university student had left Tripoli with a group of people to check on friends in Zawiya; he and the others were struck by bullets fired from an Apache helicopter while on foot in Zawiya's central square, the official said.
Moussa Ibrahim received the news as he was breaking his Ramadan fast with members of his family at a Tripoli hotel housing journalists. The elder Ibrahim, who was in the dining hall when he received a call, jumped from his chair, knocking it down, and ran from the room yelling.