The U.S. and its NATO-led partners insist their mission in Libya goes no further than protecting civilians threatened by their own government's guns, but as rebels regain the initiative and push to the doorstep of Moammar Gadhafi's hometown of Sirte, the protectors in effect have become an aerial arm of the rebels.

The role of the international coalition is coming under greater scrutiny following weeklong airstrikes led by the U.S., France and Britain that helped the rebels take a critical step in their advance toward Tripoli, the capital.

President Barack Obama, in a speech Monday night explaining the U.S. role in Libya, acknowledged that the military strikes allowed the rebels to drive Gadhafi's troops out of Ajdabiya and have now "stopped Gadhafi's deadly advance."

The Pentagon's lead spokesman on Libya operations, Navy Vice Adm. William Gortney, insisted to reporters Monday that the U.S. military is not coordinating with the rebels seeking Gadhafi's ouster. But he left little doubt that, by design or not, Western air power is propelling the rebels forward.

"Clearly they're achieving a benefit from the actions that we're taking," Gortney said. He displayed a chart that showed rebels advancing within 80 miles of Sirte, reflecting what he called a "pretty significant withdrawal" by pro-Gadhafi forces feeling the effects of relentless air attacks. Gortney said the number of air strikes on Libyan ground targets had risen from 91 on Friday and 88 on Saturday to 107 on Sunday — nearly half by U.S. planes.

Obama drew a sharp line Monday night between the U.S. military action and its diplomatic goals.

"While our military mission is narrowly focused on saving lives, we continue to pursue the broader goal of a Libya that belongs not to a dictator, but to its people," he said, adding that international leaders meeting in London this week will discuss the political pressures needed to oust Gadhafi.

Still, questions remain.

If the purpose of the U.N.-sanctioned military action is to protect civilians, does that include pro-Gadhafi civilians who are likely to be endangered in places like Sirte that are in the rebels' crosshairs? If not, it is difficult to see the Western intervention as a neutral humanitarian act not aligned with the rebels.

The first goal of the intervention was to prevent a massacre of civilians in Benghazi, the eastern Libyan city where Gadhafi forces were threatening to crush the rebellion two weeks ago. Gadhafi said he would "show no mercy."

That goal was quickly accomplished with a U.S.-led assault. A no-fly zone was established two weekends ago with little resistance. The U.S. and its partners then launched airstrikes on Gadhafi supply lines and other military targets not only near Benghazi but around other contested areas as well.

But the role of Western air power then went beyond that initial humanitarian aim, to in effect provide air cover for the rebels while pounding Gadhafi forces in a bid to break their will or capacity to fight.

Gortney disclosed that over the weekend U.S. Air Force A-10 Thunderbolt aircraft, designed to provide battlefield support to friendly ground forces, flew attack missions for the first time in this conflict. He refused to say where they flew or provide other details. Also joining the battle, he said, were Air Force AC-130 gunships, a low-flying aircraft armed with a 105mm howitzer and a 40mm cannon. Those two types of aircraft give the U.S. more ability to confront pro-Gadhafi forces in urban areas with less risk of civilian casualties.

Even though the rebels are advancing, Gortney cautioned that because they are not well-organized, their gains must be considered "tenuous."

Military officials have been careful to say their jurisdiction stops at protecting civilians, since that is the mandate of the United Nations on March 17. Obama has gone further, saying that Gadhafi is an illegitimate ruler who must step aside, and the Obama administration has struggled to explain the different rationales to the public and Congress.

U.S. officials are leery of appearing to intervene in Libya's internal conflict, and mindful that to maintain Arab and U.N. support the mission must not look like overt meddling by outsiders. It remained unclear how far the NATO intervention will go, now that the rebels are again on the offensive and Gadhafi's forces seem to be in retreat. Obama said Monday, hours before addressing the nation on Libya, that U.S. involvement will be "limited, both in time and scope."

How best to help the opposition will be a topic at a major international conference on Libya's political future on Tuesday in London. Secretary of State Hillary Rodham Clinton was representing the United States.

In his first news conference since assuming command of the Libya operation as commander of NATO's Allied Joint Force Command, Canadian Lt. Gen. Charles Bouchard on Monday said NATO was not taking sides.

Asked where NATO drew the line between protecting the civilians and aiding rebels, Bouchard said his mission was clear:

"Our goal is to protect and help the civilians and population centers under the threat of attack," he said.

The U.S., at the direction of its African Command chief, Gen. Carter Ham, had been overseeing that mission. But on Sunday NATO's 28 member nations agreed to take it over — a transition that Obama said should take place Wednesday. The United States will retain a substantial role, particularly in providing the aerial refueling and surveillance and reconnaissance that support enforcement of the no-fly zone over Libya and attacks on Gadhafi's forces.

NATO officials have said the alliance's operations, approved for up to three months, could be extended if necessary.

The U.N. Security Council approved "all necessary measures" to protect "civilians and civilian populated areas under threat of attack," and excluded "a foreign occupation force of any form." Obama has repeatedly ruled out inserting ground troops.

U.S. officials have said they are considering arming the rebels but have reached no decision.


Associated Press writers Matthew Lee, Donna Cassata and Lolita Baldor in Washington, Nicole Winfield in Naples, Italy, and Slobodan Lekic in Brussels contributed to this report.