As warplanes from the U.S. and the United Arab Emirates pounded Islamic State fighters near the Syrian city of Kobani for a third day, the U.S.-led military campaign began running up against the limits of what air power can accomplish.
"Airstrikes alone are not going to save the town of Kobani," Rear Adm. John Kirby told reporters at the Pentagon on Wednesday, adding that the militants "are going to continue to grab ground, and there are going to continue to be villages, towns and cities that they take" in Iraq and Syria.
Kirby's frank acknowledgment came after nine weeks of bombing by the U.S. and its allies, which has not stopped Islamic militants from claiming new territory in both Syria and Iraq, a setback that military officials blamed on the poor performance of Iraqi and Syrian forces battling them on the ground.
Some 500 miles east of Kobani, the limits of U.S. air power are also becoming apparent near Baghdad, where Islamic State fighters are making a less dramatic but potentially more dangerous push to take control of towns and districts within an hour's drive of the Iraqi capital, U.S. officials said.
Despite an intensifying air campaign in Fallouja and other cities not far from Baghdad, an effort that in recent days has included use of U.S. attack helicopters, the Iraqi army has continued to lose ground to the militants, U.S. officials acknowledged.
Military experts say the capital is not in immediate danger, noting that airstrikes to the south of Baghdad had shown signs of blunting attempts by militants to encircle the city. Pentagon officials hope the campaign to roll back the militants' gains will regain momentum now that U.S. special forces teams are advising Iraqi commanders and sharing intelligence with at least a dozen Iraqi army and Kurdish units.
In August, during the first days of the U.S.-led campaign against Islamic State fighters, bombing helped Iraqi and Kurdish troops regain control of the Mosul dam and halted assaults that threatened Irbil, capital of the semiautonomous Kurdish region in northern Iraq.
But the meager results since those early victories could have far-reaching implications, increasing pressure on President Obama to reconsider the strict limits he has placed on the role U.S. troops can play on the ground.
The U.S., along with Arab and European countries, has carried out 280 airstrikes in Iraq and 121 attacks in Syria since Aug. 8, according to U.S. Central Command, which oversees military operations in the Middle East.
The bombing has destroyed dozens of armored vehicles, artillery pieces, armed trucks, headquarters buildings and camps and killed hundreds of Islamic State fighters.
But the fall of Kobani to the militants would make it harder for the U.S. to recruit the rebel fighters in Syria whom the U.S. and its allies hope to turn into an effective fighting force over the next year, said Jeffrey White, a former Middle East analyst at the Defense Intelligence Agency.
"It will be seen as a defeat for the U.S., even though our [airstrikes in Kobani] have been limited until recently," White said. "It will be seen as the U.S. lacking the resolve to get the job done in Syria."
In Kobani, Kurdish fighters had been battling militants for months without help from the U.S. or neighboring Turkey, to which tens of thousands of refugees have fled.
The U.S. stepped up bombing after it became clear that the militants had moved large amounts of equipment and fighters to the outskirts of the city, one of the last areas not under their control along the Syria-Turkey border.
U.S. officials acknowledged that the air attacks were not being carried out in coordination with the Kurdish fighters on the ground, limiting their effectiveness, and that they had little faith that the city's defenders could hold out much longer.
The airstrikes are seeking to "relieve some pressure around Kobani," said a senior military official. But he added that, unlike in Iraq, "we do not have a partner that we are working with on the ground there." Turkey, which has a large army, has so far declined to use it against the Islamic State fighters.
The threat to Baghdad is different, Pentagon officials said.
"Baghdad is still protected. It's still defended. Now, that doesn't mean it's not coming under threat," said Kirby. "It doesn't mean that [Islamic State] still doesn't have designs on the capital city. They do."
Airstrikes "around the city, particularly to the south and to the southeast … have been effective in blunting" the group's "continued probing of the capital city itself," he said.
If Islamic State fighters make further inroads in threatening Baghdad, pressure on the White House to deepen the U.S. military involvement will also intensify, officials acknowledged. About 1,600 U.S. troops are in Iraq, most of them in and around the capital, and hundreds more Americans are assigned to the U.S. Embassy in Baghdad, a presence that would probably force Obama to act if security worsened substantially.
The most likely threat Baghdad faces in coming months will not be a direct military assault, according to military officials familiar with intelligence assessments of the threat.
Instead, Islamic State's efforts to control the ring of towns and roads outside the capital is seen as a way for the Sunni Arab extremist group to make it easier to step up suicide attacks and targeted killings in Shiite neighborhoods inside the city.
Fanning of sectarian tension in Baghdad could threaten the U.S. goal of persuading the Shiite-led Iraqi government of Prime Minister Haider Abadi to share power with Sunnis and Kurds, which U.S. officials say is crucial to defeating Islamic State.
With power-sharing in Baghdad, as well as new weapons and cash payments, U.S. officials hope to peel away the Sunni tribes that have joined Islamic State's ranks, officials said.
Pentagon officials have warned for weeks against overestimating the effect of air power, and they defended the military strategy Wednesday. The decision to keep U.S. troops out of a ground combat role means that ousting Islamic State fighters from many of the towns they have occupied in Iraq will take a year or more and that additional years will be needed to defeat them in their home base in Syria, the officials said.
"This will take time unless we want to own it completely," said a senior military officer who agreed to discuss the operation in return for anonymity.
The limits on the U.S. military already have caused friction between the White House and the Pentagon leadership, and tension has the potential to grow if results of the campaign don't improve in the coming months.
Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said last month that he would consider recommending to Obama that he allow U.S. advisors to accompany Iraqi army units on combat missions, in part to help direct airstrikes, if he felt that was necessary.
Obama on Wednesday made a rare visit to the Pentagon for meetings with Defense Secretary Chuck Hagel and senior commanders that included discussion of the military campaign in Iraq and Syria, Kirby said.