In a statement made Thursday night, President Obama said he has authorized military strikes on Islamic State militants if they continue their advancement on the city of Irbil, where military personnel and the U.S. consulate are located. (AP)

In a statement made Thursday night, President Obama said he has authorized military strikes on Islamic State militants if they continue their advancement on the city of Irbil, where military personnel and the U.S. consulate are located. (AP)

U.S. military aircraft carried out airstrikes on Islamist militants besieging Kurdish forces in northern Iraq, the Pentagon announced Friday.

The airstrikes targeted artillery being used by militants of the Islamic State extremist group against Kurdish forces defending Irbil, the Kurdish regional capital, the Pentagon said. It said the artillery was used “near U.S. personnel.”

The U.S. action came after President Obama authorized airstrikes against Sunni Muslim extremists who punctured Kurdish defenses in a powerful offensive in northern Iraq on Thursday. Obama also sent U.S. military aircraft to drop food and water to besieged Iraqi civilians in the region.

Obama, in a statement delivered at the White House late Thursday, said that strikes would be launched against extremist convoys “should they move toward” the Kurdish capital of Irbil, where the United States maintains a consulate and a joint operations center with the Iraqi military.

“We intend to take action if they threaten our facilities anywhere in Iraq . . . including Irbil and Baghdad,” he said.

View Graphic Map: U.S. airstrikes in Northern Iraq

Authorization for airdrops — an initial round of which was completed just before Obama spoke — and for potential airstrikes was a major development in the Iraq crisis that began in June.

A senior administration official described the airstrike authorization as “narrow,” but outlined a number of broad contingencies in which they could be launched, including a possible threat to U.S. personnel in Baghdad from possible breaches in a major dam Islamist forces seized Thursday that could flood the Iraqi capital.

U.S. aircraft also are authorized to launch airstrikes if the military determines that Iraqi government and Kurdish forces are unable to break the siege that has stranded tens of thousands of civilians belonging to the minority Yazidi sect atop a barren mountain outside the northern town of Sinjar.

“As we can provide air support to relieve that pressure, the president has given the military the authority to do so,” the senior official said. He said that congressional leaders had been consulted, but that Obama had the legal authority as commander in chief to launch the strikes to protect U.S. personnel and national security interests.

Obama has sent more than 700 U.S. troops to Iraq since June to protect the U.S. Embassy and international airport in Baghdad and facilities in Irbil, and to assess the capabilities of Iraqi forces.

But he repeated his pledge that no ground combat troops would be returned to Iraq, where the last U.S. forces withdrew at the end of 2011.

“I know many of you are concerned about any military action in Iraq, even limited strikes like these,” he said in remarks directed at the American people. “I will not allow the United States to be dragged into fighting another war in Iraq.”

1 of 42 Full Screen Autoplay Close Aug. 10, 2014 Aug. 9, 2014 Saturday Aug. 7, 2014 Thursday Aug. 5, 2014 Tuesday Aug. 4, 2014 Monday Aug. 3, 2014 Sunday Skip Ad × U.S. airdrops to aid Iraqis fleeing Islamic State forces View Photos Iraqi civilians fled as mass panic set in with the retreat of Kurdish forces from Islamic State militants. Meanwhile, President Obama approved humanitarian airdrops to besieged Iraqis escaping the Sunni extremists. Caption After being stranded on the parched Mount Sinjar for almost a week and then walking 12 miles to seek refuge in Syria, some of the persecuted civilians were able to safely return to the Kurdish region of Iraq with the help of Syrian Kurdish forces. Aug. 12, 2014 Displaced Iraqis from the Yazidi community gather for food at the Nowruz camp in Derike, Syria. Khalid Mohammed/AP Buy Photo Wait 1 second to continue.

In a statement on the initial airdrops of assistance to the Sinjar civilians, the Defense Department said: “This mission was conducted from multiple airbases within the U.S. Central Command area of responsibility and included one C-17 and two C-130 aircraft that together dropped a total of 72 bundles of supplies. They were escorted by two F/A-18s also from an airbase within Central Command; the supply mission did not require any U.S. ground forces.”

The Central Command includes most of the Middle East and South Asia, where the United States maintains military installations.

A second senior administration official, one of three who briefed reporters on the new authorizations on the administration-imposed condition of anonymity, said that the airdrops included enough food and water for 8,000 people and that further shipments were planned.

“When we face a situation like we do on that mountain . . . and when we have the unique capabilities to help avert a massacre, I believe the United States of America should not turn a blind eye,” Obama said. In the briefing, officials referred to attacks against the Yazidis as “genocide.”

The administration’s swift change in policy, following weeks of reluctance to launch airstrikes, came after fighters from the Islamic State, an al-Qaeda offshoot that has taken over much of northern and western Iraqi, turned their sights this week on the semiautonomous Kurdish region in the northeast. Although Iraqi military forces have struggled to make headway against the well-armed militants, the Kurdish region has been spared until now and has been under the protection of its own military, known as the pesh merga.

But civilians fled and mass panic set in early Thursday when Kurdish forces retreated from Qaraqosh, the largest Christian town in Iraq, and the surrounding area, putting militants within about 40 miles of Irbil.

The Islamic State also appeared to have made significant headway in efforts to seize the Mosul Dam on the Tigris River, an ailing structure whose breach could imperil the lives of hundreds of thousands of Iraqis — and everyone else in its path — in devastating floodwaters.

U.S. officials said that the administration is stepping up its military assistance to Iraqi forces and will provide aid to the pesh merga, another action that has been resisted until now as U.S. diplomats have tried to keep Iraq’s warring regions together under one flag.

The Kurds have pleaded for international assistance as they increasingly lose control of the 650-mile border between them and territory already controlled by the militants.

Extremist advances against Kurdish forces over the past week have pushed into some of the most religiously and ethnically diverse areas of Iraq, sending minorities, including Christians as well as Yazidis, fleeing from forces that have executed those they consider apostates.

The Kurdish military withdrawals have highlighted the fragility of the region’s defenses. Known as some of the fiercest and most professional fighters in the region, the pesh merga now complain of being short on ammunition and outgunned by militants who have seized caches of advanced U.S. military equipment from the Iraqi army.

“What took place was a tactical retreat,” said Brig. Gen. Azad Jalil, a pesh merga commander in the area, describing withdrawals from Qaraqosh and nearby Bartella. Thousands of Christians already had fled to Qaraqosh from Mosul after the extremists gave them three choices: convert to Islam, remain Christian but pay special taxes, or be killed.

A senior official said that more comprehensive assistance would be offered to Iraq as soon as it has chosen an “inclusive government,” a direct reference to the U.S. desire to see Prime Minister Nouri al-Maliki replaced with another leader representing Iraq’s Shiite majority.

Following an election last spring — in which Maliki’s party won more votes than any other — the new parliament has chosen a president and speaker. It is expected by Sunday to elect a prime minister, a job that Maliki has said he intends to keep.

Morris reported from Baghdad. Mustafa Salim in Baghdad and Ahmed Ramadan in Beirut contributed to this report.