The Pentagon, meanwhile, said the U.S. Air Force carried out its first Predator missile strike in Libya on Saturday, but gave no details. Libyan government officials showed evidence of an airstrike near Gadhafi's compound in Tripoli that it said caused no injuries, but it was not clear if that site was the Predator's target.
Opposition forces in Libya's third-largest city had held firm after being pounded by the government's heavy weapons for weeks. On Friday, a top Libyan official said troops would be withdrawn and local tribes would take up the fight - a notion scoffed at by rebels.
A rebel activist in the Misrata questioned how much support Moammar Gadhafi had among the local tribes.
"This whole move is just to buy time," he added, expecting further attacks.
For now, however, most of the city of 300,000 people was calm, with rebel forces taking over several key buildings that had been filled with government soldiers, including snipers. An eight-story insurance building - pockmarked by shells and scorched around the windows - had been used by snipers because it was the tallest in central Misrata and commanded a view of the city.
"After they heard the news, people began breathing freely. The women were making ululations and they went onto the streets beeping their car horns," said the activist, who asked to remain anonymous for fear of reprisal.
The only fighting Saturday was on the eastern outskirts of the city, where about 150 pro-Gadhafi soldiers trying to withdraw were fighting rebels, he said, adding that ambulances were picking up dead and injured.
Deputy Foreign Minister Khaled Kaim sought to portray the move as a decision by tribal leaders to give the army an ultimatum to step aside if it cannot retake control of Misrata.
The tribal leaders would fight the rebels if the opposition forces don't surrender, Kaim said late Friday night.
"We will leave it for the tribes around Misrata and the Misrata people to deal with the situation in Misrata," Kaim told reporters.
However, Misrata is not known to have very large or dominant tribes, further casting doubt on how effective they might be in fighting the rebels.
Hundreds of people have been killed in clashes between rebels and government forces in the city.
In the capital of Tripoli, two missiles apparently fired by NATO warplanes struck near Gadhafi's sprawling compound in the early hours of the morning, causing no injuries.
Reporters were taken to an unpaved plot next to the Bab Aziziyeh compound and shown two craters, apparently from the missiles that had pierced through thick layers of reinforced concrete, laying bare what looked like a bunker system.
Libyan officials said the space was a parking lot but a series of olive-colored metal boxes near the crater suggested it was being used for military activities.
It was not clear if the site was hit by missiles from a U.S. Predator drone. A Pentagon spokesman, Navy Capt. Darryn James, said the first drone airstrike occurred Saturday but gave no details.
In the east of the country, NATO strikes Saturday smashed more than two dozen sedans and pickup trucks belonging to government forces about halfway between Ajdabiya and Brega, said rebel battalion commander Col. Hamid Hassy.
The front in the east has been stalled between the strategic oil town of Brega and Ajdabiya for weeks.
On Thursday, Defense Secretary Robert Gates said President Barack Obama had approved the use of armed Predator drones to improve the precision of strikes on Libyan government forces. Predators had previously been used in Libya only for surveillance. The low flying Predators have been used in Afghanistan to kill militants and are suited for urban combat.
NATO stepped into the Libyan fighting in mid-March, unleashing airstrikes against Libyan military targets as part of a U.N. mandate to protect civilians.
Meanwhile, an Italian-owned tugboat was released after being held in Libya for weeks, the ship owner and the Italian Foreign Ministry said Saturday.
The Asso 22 left Friday night was expected home Sunday in Italy, with its crew of eight Italians, two Indians and a Ukrainian unharmed, according to Naples-based Augusta Offshore SrL.
The ship had been occupied by Libyan military officers since mid-March and had for the most part been docked at Tripoli. After it left, the Italian vessel made contact with an Italian navy ship in the Mediterranean as part of the NATO operations in Libya, Augusta said.
Ship owner Mario Mattioli of Augusta told Sky Italia that no ransom had been paid and that diplomacy "at the top level" had helped resolve the case. The Foreign Ministry expressed satisfaction.
It wasn't clear if the seizure amounted to Libyan retaliation for Italy's participation in enforcing the U.N.-mandated no-fly zone over Libya. Italy, Libya's former colonial ruler, has allowed use of its bases by coalition aircraft and has offered its own jets for missions.
Hadid reported from Cairo. Associated Press writer Sebastian Abbot in Benghazi, Libya, and Maggie Michael in Cairo contributed to this report.