TRIPOLI, Libya — Libyan rebels claimed Friday that they have recaptured the center of the besieged western city of Misurata, partly thanks to weeks of NATO airstrikes, and said they hoped deployment of U.S. armed Predator drones could help them drive Moammar Gaddafi’s forces out of the city completely.

Further east, in the rebel stronghold of Benghazi, Sen. John McCain (R-Ariz.), one of the strongest congressional proponents of U.S. military intervention in Libya, made an unannounced visit to assess the situation for himself and called the rebels his heroes.

Rebels were buoyed by signs of progress in their military struggle against Gaddafi, seizing control of a border crossing with Tunisia near the country’s western mountains and, they said, reclaiming the center of Misurata.

Adm. Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, said coalition airstrikes have degraded Gaddafi’s ground forces by 30 to 40 percent but that the conflict nevertheless was “certainly moving towards a stalemate.”

In Misurata, though, the mood has lifted after weeks of increasingly desperate calls for more international help. Gaddafi’s forces seemed to be in disarray in Misurata, said Mohamed, a spokesman for the city council, who asked that his full name be withheld for safety reasons. Misurata, Libya’s third-largest city 131 miles east of Tripoli, has resisted a Gaddafi counteroffensive for more than a month, becoming the last remaining rebel stronghold on Libya’s western Mediterranean coast.

“There is a general pattern of collapse everywhere,” Mohamed said, speaking via Skype. “According to our fighters, they [Gaddafi’s troops] seem to be acting like headless chickens, because their command and control has been disrupted by NATO.”

Mohamed said rebels on Thursday cleared the last three buildings in central Misurata where government snipers had been operating, and he said the city was now “sniper free.”

The rebel account could not be independently verified, and Gaddafi’s government says it still controls 80 percent of the city. However, videos released by the rebels in Misurata showed their flags flying over pockmarked and charred high-rise buildings in the city, with fighters walking through streets strewn with glass and rubble, waving their hands in the air triumphantly and shouting Allahu Akbar (God is greatest).

Mohamed said the rebels had killed around 100 government soldiers in Misurata on Tuesday and scores since then. The rebels now control all of the city center and its main Tripoli Street, apart from a group of Gaddafi’s troops holding out in the main hospital who were surrounded and being asked to surrender, he said.

“I walked all the way down Tripoli Street myself this morning, all the way to the hospital,” he said. Mohamed and doctors in the city had expressed growing frustration with NATO in past week, but on Friday he said that if not for the alliance, Misurata would have been overrun a long time ago.

Mohamed said the rebels have secured the roads leading east and west of the city to prevent Gaddafi from sending in reinforcements but have not yet secured the road leading south to Bani Waled.

Residents in Misurata complain of water shortages and a lack of goods ranging from baby food to vegetables. They say electricity in the city has been cut off, forcing them to rely on generators. Thousands of stranded foreign migrant workers are awaiting evacuation in the port area.

There has also been intense fighting in the country’s remote western mountains in the past week, and rebels seized control of the border crossing to Tunisia nearest the area on Thursday. The government claimed that its military regained control of the border post later in the day, but witnesses said this was untrue, with the rebel flag still flying over the post on Friday.

In Benghazi, McCain, the top Republican on the Senate Armed Services Committee walked through the streets on Friday and was due to meet the rebel civilian and military leadership later in the day. He said he was there “to get an on the ground assessment of the situation.”

McCain has pushed for the United States to arm the rebels and has criticized the Obama administration’s decision to take a back seat in NATO’s campaign of airstrikes. On Thursday, though, the United States took a step toward further involvement in the conflict, flying armed Predator drones over Libya for the first time.

The drones were forced to turn back Thursday because of bad weather, and Mohamed, the rebel spokesman in Misurata, said the weather there was bad again on Friday.

Officials said the U.S. military would maintain at least two of the unmanned aircraft over Libya at all times. The drones have been used extensively in Pakistan and other areas where U.S. forces have no troops on the ground. They can stay aloft for hours without being noticed from the ground and hit targets with missiles, and officials say they are well suited to urban warfare in places like Misurata.

Gaddafi’s government says the rebels are led by al-Qaeda militants and gangsters, and it argues that the Islamist radicals will only get stronger the longer the conflict drags on.

But Mullen, addressing U.S. troops during a visit to Baghdad, played down those concerns, Reuters news agency reported.

“It certainly doesn’t mean, whether it's Libya or in other countries, that there aren’t leaders in terrorist organizations that aren't looking to try to take advantage of this,” Mullen said. “But we're watchful of it, mindful of it, and I just haven't seen much of it at all. In fact, I've seen no al-Qaeda representation there at all."

Mullen acknowledged that the Libyan Islamic Fighting Group, which waged a failed armed insurgency against Gaddafi's rule in the 1990s, had “stirred a little bit.” But he added, “I haven't seen anything significant at this particular point in time,”