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This image from Associated Press video shows smoke rising from airstrikes targeting Islamic State militants outside the city of Erbil in northern Iraq on Friday. Associated Press
The U.S. military launched a series of airstrikes in northern Iraq on Friday as American forces returned to action in Iraq to fight a brutal Sunni extremist force accused of attempting genocide in its bid to create a hard-line Islamic state.
U.S. fighter jets and armed drones attacked targets in Iraq for the first time since the American troop withdrawal in 2011 to try to halt the Sunni extremist advance on the Iraqi Kurdish capital of Erbil.
The initial targets of the U.S. strikes—artillery, a group of fighters and a convoy of vehicles—were modest. Further attacks expected in coming days may remain relatively small, allowing the Obama administration to stick to its pledge of limited involvement.
Iraqi Kurdish Peshmerga fighters on the front line in Khazer, near the Kurdish checkpoint of Aski kalak, on Friday. TK
However, the U.S. faced the prospect of having to intensify the air offensive if militants, undeterred, continue to press their attack against fleeing and trapped religious minorities and the Kurdish-dominated city of Erbil.
The airstrikes are meant to provide critical support for Kurdish forces struggling to repel militants from the group calling itself the Islamic State, also known as ISIS or ISIL. The militant forces have taken control of the country's largest dam and have beheaded Iraqi soldiers and driven thousands of religious minorities into desolate mountains where they are struggling to survive.
"If there is American military might that can be deployed to tip the balance in support of Kurdish forces that are operating on the ground, then we will certainly look for an opportunity to do that," White House spokesman Josh Earnest said Friday.
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As the U.S. military strikes unfolded, U.S. officials continued pressing for speedier progress in Baghdad toward formation of a new Iraqi government, a step they repeatedly have said is a key prerequisite for stability in the country.
Speaking in Kabul, Secretary of State John Kerry said the solution for Iraq's problems remains a political deal in Baghdad to form a unity government, but that the U.S. has made it clear it will act.
"President Obama has been unequivocal that he will do what is necessary when it's in our interest to confront ISIL and its threat to the security of the region and to our own security in the long run," Mr. Kerry said.

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Vice President Joe Biden, in a phone call Friday with new Iraqi President Fuad Masum, stressed the need for a new government as soon as possible.
U.S. jet fighters hit Islamic State targets hours after President Barack Obama approved the plan, citing a need to protect American personnel working in the region and prevent militants from decimating Iraq's marginalized Yazidi religious minority.
In the regional Kurdish capital of Erbil and in the northern city of Dohuk, where tens of thousands of people have taken refuge from Islamic State militants, people were celebrating.
What's News: US jets dropped 500-pound, laser-guided bombs on Islamic State militants in Iraq. WSJ's Lee Hawkins reports.
"The situation is better today than it was yesterday and people are returning to their homes," said Abdullah Hawez, a student in Erbil. "But it feels like this threat almost came out of nowhere. We had felt so secure but things have changed."
The first laser guided 500 pound bombs fired by F/A-18 jet fighters destroyed mobile artillery unit outside Erbil, U.S. defense officials said.
Hours later, an armed MQ-1 Predator drone twice struck an Islamic State mortar position outside the city.
A third strike by four F/A-18 fighter planes dropped eight bombs on a seven-vehicle convoy and a stationary mortar position, the Pentagon said.
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President Barack Obama speaks with Jordan's King Abdullah II from the Oval Office on Friday. European Pressphoto Agency
The F/A-18s flew from the USS George H.W. Bush, an aircraft carrier in the Persian Gulf. Officials said the drones were from a U.S. base in the Middle East. Before Friday, the last U.S. strike in Iraq was in July, 2011, military officials said.
Pilots flying the bombing missions weren't given a green light to strike targets at will, but were executing missions under orders from Gen. Lloyd Austin, the commander of U.S. forces in the Middle East, who has broad latitude within Mr. Obama's authorization to choose targets, officials said.
U.S. officials expect airstrikes to continue in the coming days, along with emergency military airdrops of food and water. On Thursday, cargo jets dropped tons of supplies to help Iraqi refugees who have been pleading for help as women and children suffer from thirst.
U.S. jet fighters hit Islamic State artillery positions in northern Iraq on Friday, the first of what is expected to be a series of American strikes to halt the Sunni extremist advance on the Kurdish capital of Erbil. WSJ's Julian Barnes has the details. Photo: Getty
Mr. Obama said that the Sunni extremists appeared poised to wipe out the Yazidis in an act of genocide.
Military officials said most of the initial supplies made it to the refugees. But it could take several days to determine if the airdrop was effective or if more supplies are needed.
Now that airdrops have started, the United Nations in Iraq is preparing to establish a humanitarian corridor to allow people to flee threatened areas, said Nickolay Mladenov, the U.N.'s secretary-general's special representative for Iraq.
Mr. Obama said he has given his authorization for U.S. aircraft to strike militants who interfere with efforts to aid the refugees.
"The enemy gets a vote," said a senior defense official. "If they stop, we stop. If they attack we bring down the hammer."
The push deeper into Northern Iraq by the Islamic State has put the group less than 40 miles from the Kurdish capital of Erbil and sent tens of thousands fleeing.
The Islamic State remains a puzzle for many U.S. officials. The U.S. was caught off guard by the most recent advance, not the first time the militant movement has confounded U.S. expectations. Some believed the militants were headed for the capital Baghdad.
U.S. officials expected the Sunni militants to avoid a direct assault on the Kurdish stronghold because their fighters are seen as a more effective force than the Iraqi army.
The continuing advance could be meant to test the strength of the Kurdish forces or assess the willingness of Baghdad's central government to come to the aid of the Kurds, these officials say.
Another official said the offensive could be a feint by the group, disguising its preparations for a more major attack elsewhere. One defense officials said the group appears to be securing supply lines and highways that run both north and south and east and west.
Key lawmakers backed Mr. Obama's decision and urged him to deepen American involvement in Iraq to defeat the Islamic State.
"This is not a typical terrorist organization," said U.S. Sen. Dianne Feinstein (D.-Calif.). "It is a terrorist army, operating with military expertise, advancing across Iraq and rapidly consolidating its position."
House Speaker John Boehner (R., Ohio) on Friday endorsed Mr. Obama's decision on strikes, but he lambasted the White House as "parochial" and "disengaged" for not acting sooner or more aggressively.
Meanwhile, the U.S. government on Friday said airlines should stop flying over Iraq. All flights are being blocked "due to the potentially hazardous situation created by the armed conflict between militants associated with the Islamic State in Iraq and the Levant and Iraqi security forces and their allies," the U.S. Federal Aviation Administration said in a safety bulletin.
—Jeffrey Sparshott, Felicia Schwartz and Michael R. Crittenden contributed to this article.
Write to Dion Nissenbaum at dion.nissenbaum@wsj.com