BENGHAZI, Libya » U.S. Sen. John McCain called for increased military support for Libya’s rebels Friday, including weapons, training and stepped-up airstrikes, in a full-throated endorsement of the opposition in its fight to oust Moammar Gadhafi.

In the Libyan capital, meanwhile, a senior official said government troops would step back and allow local armed tribesmen to deal with rebels in the besieged city of Misrata.

The action came a day after the U.S. began flying armed drones to bolster NATO airstrikes, and having the tribesmen take up the fight could make it harder for the Predators to distinguish them from Misrata’s civilians or the rebels.

Early Saturday, loud booms were heard in Tripoli, apparently from NATO airstrikes.

Reporters were taken to an unpaved plot next to Gadhafi’s sprawling Bab Aziziyeh residential compound in Tripoli. They were shown two craters, apparently from missiles that had pierced through thick layers of reinforced concrete, laying bare what looked like a bunker system. Eight narrow military-issue metal crates were stacked next to one of the craters.

About two dozen Gadhafi supporters arrived at the scene, waving green flags in support of the Libyan leader.

McCain, the top Republican on the Senate Armed Services Committee, said the United States and other nations should recognize the opposition’s political leadership as the "legitimate voice of the Libyan people." The White House disagreed, saying it was for the Libyan people to decide who their leaders are.

McCain also called the rebels "patriots" with no links to al-Qaida, in contrast to what some critics have suggested, and added they should receive Gadhafi assets that were frozen by other countries.

The chairman of the U.S. Joint Chiefs of Staff, Adm. Mike Mullen, said in Iraq that although the timing was hard to predict, the eventual ouster of Gadhafi and his family from power "is certain."

Rebels in the western city of Misrata raised their tricolor flag atop an eight-story building in celebration after driving pro-government snipers out of the structure Thursday. The battle-scarred building commands a strategic view of the central part of Libya’s third-largest city and the key main thoroughfare of Tripoli Street. The snipers had terrorized residents and pinned down rebel fighters.

As a result, the number of civilian casualties dropped dramatically Friday for the first time in several weeks, said one rebel who spoke on condition of anonymity because he feared retaliation.

"Spirits are high but the military situation is still unknown," he said. "The rebels easily entered yesterday, so it was clear that the Gadhafi forces quickly withdrew."

Although there was less fear about snipers, fighting was still taking place near Misrata’s central hospital and the vegetable market, a rebel said.

In Tripoli, Deputy Foreign Minister Khaled Kaim said tribal leaders had given the army an ultimatum, saying it must step aside if it cannot retake control of Misrata, which has been besieged by Gadhafi’s forces for two months.

The tribal leaders would fight the rebels if they don’t surrender, Kaim said late Friday night.

Asked if that meant troops would get out of the way, he said: "This is how I imagine it would happen." However, he said negotiations between the military and tribal leaders are continuing.

Kaim did not say when the military would pull back from Misrata or when the armed tribesmen would move in. "We will leave it for the tribes around Misrata and the Misrata people to deal with the situation in Misrata," Kaim told reporters.

Hundreds of people have been killed in clashes between rebels and government forces in the city of 300,000. The international community has accused Libyan forces of firing indiscriminately at civilian areas with tanks, rockets and mortars.

NATO’s air campaign has been largely unable to strike at the government forces because of their proximity to civilians, and the rebels have complained that NATO’s strikes have not done enough. McCain also has been critical of the U.S. decision to turn over control of the operation to the military alliance.

On Thursday, the U.S. began flying armed drones that are "uniquely suited for urban areas," said U.S. Marine Gen. James Cartwright. The drones can fly lower and counter the pro-Gadhafi forces’ tactic of traveling in civilian vehicles that are difficult to distinguish from those of rebel forces. Thursday’s first mission, however, was forced to turn back due to poor weather without firing any of its Hellfire missiles, Cartwright said.

Kaim denounced the U.S. move as a "dirty game."

"This will be another crime against humanity committed by the American administration, and I feel really very sad for President Obama to be involved in such things," he said.

At a news conference in the rebels’ stronghold of Benghazi ini eastern Libya, McCain said he did not believe that the United States should send in ground troops, but it should be much more involved in the air campaign and "facilitate" the arming and training of the rebels — much as it armed the mujahedeen who fought the Soviets in Afghanistan in the 1980s.

"We need to urgently step up the NATO air campaign to protect Libyan civilians, especially in Misrata," he said. "We desperately need more close air support and strike assets."

McCain applauded the Obama administration’s decision to use the drones "so we can better identify Gadhafi’s forces as they seek to conceal themselves in civilian areas."

McCain urged the use of combat aircraft more suited for engaging targets in urban areas, such as A-10 Thunderbolts, which are anti-tank planes, and AC-130 gunships, outfitted with heavy weaponry, including cannons, rockets and machine guns. Earlier this month, Army Gen. Carter Ham told McCain’s Senate committee that recent bad weather and threats from Gadhafi’s mobile surface-to-air missile systems hampered efforts to use those aircraft to support friendly ground troops.

All nations should recognize the opposition’s Transitional National Council as the legitimate voice of the Libyan people, McCain said, and provide it with "every appropriate means of assistance," including "command and control support, battlefield intelligence, training and weapons."

White House Press Secretary Jay Carney said the administration disagreed with McCain’s call for recognition of the rebels’ political leadership.

"We think it’s for the people of Libya to decide who the head of their country is, not for the United States to do that," Carney said aboard Air Force One as President Barack Obama returned to Washington from California.

Carney said U.S. officials had been meeting regularly with opposition leaders, including the national council, and would continue to do so to advise them as they try to prepare for a post-Gadhafi Libya.

McCain is the highest profile U.S. visitor to meet with the rebels. French President Nicolas Sarkozy has agreed in principle to travel to Benghazi, although the date has not been worked out, a top presidential aide said.

The council was encouraged by McCain’s visit, said Fathi Baja, the head of the group’s political committee. The members asked McCain to press for greater U.S. involvement in the NATO campaign.

"The United States started the action strongly. Now people feel that there is some kind of retreat," he said, expressing a common sentiment in Benghazi. "They want the United States to be the leader again."

Some in the West have raised the possibility that Islamic militants may be among the rebels, but McCain said he did not see any evidence of that.

"I have met these brave fighters and they are not al-Qaida," he said. "To the contrary, they are Libyan patriots who want to liberate their nation.

"They are my heroes," he said.

However, McCain cautioned that the situation could change if there is a deadlock on the battlefield.

"I do worry that if there is a stalemate here, that it could open the door to radical Islamic fundamentalism because of the frustration that thousands and thousands of young people would feel as they are deprived from participating in democracy in the united Libya."

Kaim, the Libyan government spokesman, said McCain’s visit was another sign that the West is "siding with the rebels," instead of sticking to the U.N. mandate of protecting Libyan civilians.

At a news conference in Baghdad, Mullen told reporters that the battle between the rebels and government forces in Libya "has become a much more difficult fight."

"I have observed in recent days essentially it is very much stalemate-like in the vicinity of Ajdabiya and Brega" — cities in eastern Libya, which is largely controlled by the rebels. Gadhafi’s forces control most of western Libya.

He said it was not surprising that "the regime forces have changed their tactics," Mullen said.

"The exact outcome of when something is going to happen is very difficult to predict. But I think the eventual outcome is certain," Mullen said, referring to the ouster of Gadhafi and his family.

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.

The latest voyage, which will also bring 160 tons of food, medical supplies, tents and mattresses to residents trapped in the city by the fighting, 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 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 tricolor 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.

The takeover of the crossing opened an important supply line for the rebels to their stronghold in Libya’s western Nafusa mountain area, near the border with Tunisia.