(CNN) -- Ousted Libyan leader Moammar Gadhafi's hometown of Sirte will fall soon, perhaps within days, commanders of the anti-Gadhafi operation told U.S. Defense Secretary Leon Panetta on Friday, according to a senior U.S. defense official traveling with him.
Panetta met during the morning with the commanders at the naval base that hosts the U.S. Sixth Fleet in Italy, the official said.
The commanders said they have no reason to believe Gadhafi can exercise command and control of those militia members who remain loyal to him, the official said.
They further believe that, although the anti-Gadhafi forces are gaining the ability to exercise control, they will likely need training to develop their capabilities, the official said.
Still, no timetable has been drawn up for when commanders will recommend that NATO forces end their involvement, the official said.
The fall of Sirte could not come soon enough for Libya's new leaders, eager to declare liberation once the birthplace of Gadhafi is under their control.
But battles for the coastal city southeast of Tripoli have raged for weeks as Gadhafi loyalists dug in to put up stiff resistance.
Complicating the matter was the resignation Friday of Mahdi al-Harati, the deputy head of the Tripoli Military Council, a senior National Transitional Council official said. "He resigned due to differences with the NTC on the planning of the security of Tripoli. We are the official governing body and the efforts of the revolutionaries that fought for the liberation are appreciated but the command must be centralized," Mohamed Sayeh told CNN.
He said NTC officials were trying to get that message across "in a democratic, brotherly manner."
Al-Harati will continue as commander of the Tripoli brigades, said Fathi al-Wersali, a senior member of the Tripoli Military Council. "There is overlapping in the role of the Tripoli military council and the NTC," he said. "A clear mechanism has not been finalized, which leaves us not clear on how to move forward in securing Tripoli."
Early Friday, hundreds of revolutionary fighters attacked from the west, NTC military field commanders said.
Gadhafi's men control tall buildings in the city center, where they fire on their foes from rooftops. They were striking with rocket-propelled grenades and machine guns, said the council's commanders, Mohammed Ibrahim and Jamal al-Raeis, from the front lines.
At least 12 revolutionary fighters were killed and 193 others wounded Friday, the Misrata Military Council said.
"The battle will be difficult, but we have to finish it," Ibrahim said.
The International Committee of the Red Cross evacuated three wounded people from Ibn Sina hospital in Sirte to a field hospital on Thursday.
Dibeh Fakhr, an ICRC spokesman in Misrata, said Friday that the group is committed to re-entering Sirte to evacuate more casualties.
The Red Cross said thousands of civilians remain inside Sirte and waves of war-weary civilians were streaming from the coastal city every day.
"We even saw entire families leaving on foot, bringing their small children with them, without any food or water," Red Cross delegate Ghafar Bishtawi said.
More than 18,000 people, including many women, children and elderly people, are displaced east of Sirte and hundreds have moved to safer locations west of the city, the Red Cross said.
Sirte is one of two contested cities remaining in Libya as the National Transitional Council moves forward to form new governance in the country.
The council's leader and the interim prime minister have promised to step down to clear the way for a new government once Sirte is taken.
Gadhafi, wanted by the International Criminal Court in the Hague for alleged crimes against humanity, has not been seen in public in months. Syrian-based television aired an audio message Thursday that was purportedly from the deposed leader. In it, the speaker urged Libyans to protest the new leadership.
CNN's Mohammed Tawfeeq and journalist Mohamed Fadel Fahmy contributed to this report.