The next move may be up to the Islamic State group, the al-Qaida inspired extremists.

About three dozen U.S. military trainers and a U.S. consulate are in Irbil, where Kurdish forces are fighting off a militant advance.

Defense Secretary Chuck Hagel said of the Islamic State group, "They are well organized and they're armed, and they are a significant threat to the stability of Iraq.''

State Department deputy spokeswoman Marie Harf said the Islamic State group must at least halt its advance on Irbil to prevent further strikes.

Iraq has been pleading for months, if not years, for additional U.S. military help to combat the extremists, but the U.S. pulled out of Iraq in part because it couldn't reach an agreement with the government on legal immunity for U.S. troops. Harf said the Obama administration acted now out of concern that "there was a crisis that had the potential to get much worse."

U.S. officials said the Islamic State extremists in recent days have shown military skill, including using artillery in sophisticated synchronization with other heavy weapons. Their force had overwhelmed not only Iraqi government troops but also the outgunned Kurdish militia.

The Obama administration insists the airstrikes and humanitarian airdrops are not the start of an open-ended campaign to defeat the militants.

The president's critics say his approach is too narrow.

"A policy of containment will not work," Sens. John McCain and Lindsey Graham, both Republicans, said in a joint statement. They are among the chief critics of Obama's foreign policy in general, beginning with his decision to stick to the 2011 timetable set by President George W. Bush for a full withdrawal of U.S. troops.

The Islamic militants are "inherently expansionist and must be stopped," the senators said. "The longer we wait to act, the worse this threat will become."

Beyond airstrikes, the administration has been asked to provide arms directly to the Kurdish forces defending Irbil. Until now, the U.S. has been willing to do that only through the central government in Baghdad, which has long feuded with the semi-autonomous Kurdish government in Iraq's north.

Michael Barbero, a retired Army general who ran the U.S. training mission in Iraq from 2009 to 2011, said Baghdad never delivered about $200 million worth of American weapons that were designated for the Kurds. Pentagon officials maintain they can provide arms only to the Iraqi government, although Harf said Friday the Kurdish forces play a critical role in the crisis.

"We understand their need for additional arms and equipment and are working to provide those as well so they are reinforced," she said.

The CIA could supply the Kurds under a covert operation. An agency spokesman declined comment when asked whether that was happening.

In announcing his decision to intervene militarily, Obama said he would not allow the U.S. "to be dragged into fighting another war in Iraq."

The extremists control an impressive stretch of territory from the outskirts of the Syrian city of Aleppo to most Sunni-dominated areas of northern and western Iraq, up to the edges of Baghdad.

They frequently launch bombings and other attacks in Baghdad, mostly targeting Shiites and government officials, often within sight and hearing of the U.S. Embassy, which is located in the capital's heavily fortified Green Zone.

The State Department on Friday warned U.S. citizens against all but essential travel to Iraq and said those in the country were at high risk for kidnapping and terrorist violence.

"I think the administration realizes that we're dealing with that rarest of things in President Obama's world, which is a military situation that has to be resolved militarily," said James F. Jeffrey, who was the U.S. ambassador in Baghdad when American troops withdrew from Iraq in 2011. The basic problem, Jeffrey said, is "these guys have to be stopped. And it's not a matter of whether the U.S. should stop them -- it's a matter of when."

Across the Mideast, the U.S. has deployed considerable military power, including warplanes and an air operations center in the Persian Gulf state of Qatar. The aircraft carrier USS George H.W. Bush currently is located in the Persian Gulf and was the launching site for Friday's airstrikes.

The crisis appears to be falling to Washington to deal with -- despite Obama's consultations with other nations and the U.N. -- as the U.S. struggles with the parallel challenge of Islamic extremists' gains in neighboring Syria.

Vice President Joe Biden, in a call Friday to Iraqi President Fuad Masum, emphasized the threat the extremists present to all Iraqis and affirmed U.S. support, the White House said.

(AP)