DOHUK, Iraq — The United States launched a series of airstrikes against Sunni militants in northern Iraq on Friday, using Predator drones and Navy F/A-18 fighter jets to destroy rebel positions near city of Irbil, the U.S. military said Friday.

The strikes were aimed at halting the advance of militants with the Islamic State toward Irbil, the Kurdish capital, which is home to a U.S. Consulate and thousands of Americans. The action marked the return of the U.S. to a direct combat role in a country it left in 2011.

Warplanes dropped 500-pound laser-guided bombs on a number of targets: a mobile-artillery piece that was being towed from a truck and had begun shelling Irbil, a stationary convoy of seven vehicles and a mortar position.

The military also used a remotely piloted drone to strike another mortar position. After the first strike, the military said in a statement, the militants “returned to the site moments later” and “were attacked again and successfully eliminated.”

Defense officials expressed confidence they could achieve within a few days one of President Obama’s stated goals: stopping the advance of the militants on Irbil.

Less certain was whether the other objectives Obama had announced — breaking the siege on tens of thousands of refugees stranded on Mount Sinjar and protecting Americans in Baghdad — could be achieved as quickly, given Iraq’s instability.

U.S. planes also conducted a second airdrop of food and water early Saturday to those trapped on Mount Sinjar and the surrounding mountains, said Pentagon chief spokesman Rear Adm. John Kirby.

While Obama said Thursday night that he had authorized military strikes, if necessary, to help liberate the refugees on Mount Sinjar, all of the military attacks Friday were directed toward stopping the militants’ advance on Irbil.

On Friday, he said he was open to supporting a sustained effort to drive Sunni militants out of Iraq if its leaders form a more inclusive government and he vowed that the United States had no intention of “being the Iraqi air force.”

The president said he was confident the Iraqi leaders understand “the cavalry is not coming to the rescue” with ground forces. But he insisted the United States has a “strategic interest in pushing back” the Islamic State. He suggested a potentially broader mission than the one he described in Thursday’s address.

“We’re not going to let them create some caliphate through Syria and Iraq,” the president said in an hourlong interview with New York Times columnist Thomas Friedman. “But we can only do that if we know that we have got partners on the ground who are capable of filling the void.”

Lawmakers offered tempered support for the president’s actions in Iraq, but he also drew criticism from Republicans and Democrats for a mission that some called too limited and others worried would draw the United States more deeply back into Iraq.

Democrats and the anti-war groups that make up a crucial part of their political base said they were concerned about “mission creep,” cautioning that their opposition to committing U.S. ground forces in Iraq was resolute.

Obama offered his justifications for his latest use of military force in Iraq while lamenting the outcome of a similar decision he made to intervene militarily in Libya in 2011. He defended the desire to help oust the Libyan dictator, Moammar Gadhafi, with U.S. air power, but acknowledged that he had “underestimated” the chaos that would follow after U.S. forces left.

“So that’s a lesson that I now apply every time I ask the question ‘Should we intervene militarily?’ ” Obama said. “Do we have an answer the day after?”

Kurdish fighters, known as peshmerga, have been pressed hard in recent days by the militant fighters, who have seized several towns near Irbil from the Kurds and taken the Mosul Dam, one of the most important installations in the country.

“The airstrikes are being led by the USA, and peshmerga are attacking with Katyusha,” said Halgurd Hekmat, a spokesman for the Kurdish fighters, referring to a Russian-made rocket.

Fighters with the Islamic State, feeding on anger among Sunnis over their treatment by the Shiite-led government of Iraqi Prime Minister Nouri al-Maliki, took control of large pieces of northern and western Iraq in June, including Mosul, Iraq’s second-largest city. The group also controls about a third of Syria.

Islamic State fighters also seized U.S.-supplied weaponry and vehicles as Iraqi army units disintegrated or fled. So far the army and Shiite militias have managed to halt the militants’ advance outside Baghdad, the capital.

Many members of religious minorities in northern Iraq, including Christians, have fled to Kurdish territory to escape the militants, who have imposed harsh fundamentalist rule in areas they control.

Others — including tens of thousands of Yazidis, who follow an ancient faith linked to Zoroastrianism and are stranded in a mountainous area to the west — have been trapped and besieged by the militants. Delivering humanitarian aid to that group is one of the purposes of the U.S. operations in Iraq, Obama said.

Britain said Friday that it would not take part in the current military action but would provide humanitarian aid and technical assistance.

“What we have decided today is to assist the United States in the humanitarian operations that started yesterday,” the British defense secretary, Michael Fallon, said in London.

Turkey, a NATO ally that borders northern Iraq, said Friday that it, too, would increase humanitarian aid to the region, news agencies reported.

In response to the fighting, Lufthansa, Turkish Airlines and other carriers canceled flights to and from Irbil.

In the U.S., the FAA banned American carriers from flying over Iraq, saying hostilities there could threaten safety. British Airways also said it was temporarily suspending flights over Iraq.

Material from the Los Angeles Times and The Associated Press is included in this report.