The Libyan army will withdraw from the besieged city of Misrata, according to a senior Libyan government official.

Armed tribesmen would replace the army, said Deputy Foreign Minister Khaled Kaim. He provided no details on the possible military pull-out.

"We will leave it for the tribes around Misrata and the Misrata people to deal with the situation in Misrata," Kaim told reporters Friday.

Misrata has been under siege by forces loyal to leader Moammar Gadhafi for nearly two months. Hundreds of people are believed to have died in clashes between rebels and government forces.

In Misrata, opposition fighters said Friday they now control nearly all the city's downtown.

The rebels raised their red, black and green flag Thursday atop the tallest building on Misrata's Tripoli Street, a strategic avenue that divides the city into east and west and has been the epicentre of the fiercest clashes in the country's three-month-old civil war.

Forces loyal to Gadhafi had used the street's buildings as perches for sniper fire and shelling in the fight to control Misrata, the rebels' only foothold in western Libya.

"Spirits are high but the military situation is still unknown," said one rebel who spoke on condition of anonymity for fear of retaliation.

He said opposition fighters entered the eight-storey Tripoli Street building with relative ease, suggesting Gadhafi's forces had hastily withdrawn.

NATO's airstrikes on Gadhafi's forces have helped the rebels overcome their inferior firepower and training, but the rebels want the military alliance to do more. NATO officials say their air campaign is largely unable to strike at the attackers on the ground in Misrata because of proximity to civilians.

Early Saturday morning, two NATO airstrikes hit Gadhafi's compound in Tripoli, leaving behind a small crater in a parking lot. The Libyan government said three people were killed.

U.S. Senator John McCain addresses a news conference in the rebel stronghold of Benghazi on Friday. The rebels' flag flies behind him. (Amr Abdallah Dalsh/Reuters)

On Friday, U.S. Senator John McCain visited the rebel stronghold of Benghazi, in the east, where he repeated his call for his country to deploy its "unique offensive capabilities" to help the opposition oust Gadhafi.

The United States led the initial stages of the international air war on Gadhafi's arsenal but then surrendered command to NATO. It has since ramped up its effort, however, bringing in unmanned Predator drone planes that can fly low over cities and better distinguish civilians from militants.

The first Predator mission flew Thursday, but the aircraft — armed with Hellfire missiles — turned back due to poor weather without firing any of its munitions, a spokesman for the U.S. marines said.

Border crossing seized

Also Friday, a fourth ship chartered by the International Organization for Migration is leaving Benghazi to evacuate stranded migrant workers and wounded civilians from Misrata.

A rebel fighter guards the southern Libyan and Tunisian border crossing of Dehiba on Friday. Thousands of Libyans who had fled across the frontier have started to trickle back home. (Zoubeir Souissi/Reuters)

The latest voyage, which will also bring 145 tonnes of food, medical supplies, tents and mattresses to residents trapped in the city, follows three earlier evacuations of more than 3,100 people from Misrata on another IOM-chartered vessel, the Ionian Spirit.

In western Libya, rebels consolidated control over the Dhuheiba border crossing with Tunisia that they seized a day earlier, following several days of intense fighting with government troops. Libyan government officials had claimed Thursday that government troops had retaken the crossing.

However, several tricolour rebel flags fluttered from the crossing Friday, and rebel weapons, including machine-guns, were seen in the area. Thousands of Libyans had fled to Tunisia during the fighting, but many were making their way back home Friday.