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WASHINGTON (CNN) — [Breaking news update 8:58 a.m.]

U.S. military aircraft have conducted a strike on ISIS artillery that had been used near Irbil, Iraq, Pentagon spokesman Rear Adm. John Kirby said Friday on Twitter.

Two American F/A-18 aircraft dropped 500-pound laser-guided bombs on a “mobile artillery piece” used by ISIS at about 6:45 a.m. ET, Kirby said. ISIS was using the artillery to shell Kurdish forces defending Irbil, Iraq, where U.S. personnel are located, he said.

The commander of U.S. Central Command made the decision to strike under authorization granted him by President Barack Obama, Kirby said.

[Original story published 8:56 a.m.]

Obama on Thursday gave authorization to launch “targeted airstrikes” if needed to protect U.S. interests from fighters with the Islamic State, formerly known as ISIS.

The U.S. military could also use airstrikes to intervene in a humanitarian crisis that the Islamic State is inflicting on a religious minority.

The Islamic State moved closer to U.S. interests in Iraq’s Kurdish region in the north this week, taking towns from the Kurdish fighting force, known as the Peshmerga.

Before the Islamic State’s onslaught, the region had been the most stable in Iraq and a cooperative ally of the United States. U.S. military advisers and consular personnel are stationed in the Kurdish capital, Irbil.

In an address Thursday night announcing his decision, Obama said he has directed the military to strike the militants “should they move towards the city.”

Kurdish leaders have been pleading for the United States or NATO to buttress their forces against the Islamic State from the air. The President seems to have heard their appeal.

“We do whatever is necessary to protect our people,” Obama said, adding, “We support our allies when they’re in danger.”

It is now up to the Islamic State, a senior administration official said. If it decides to approach U.S. interests, airstrikes are a “clear possibility.”

Obama: Potential ‘genocide’

U.S. airstrikes could also hit the Islamic State if militants continue to endanger the lives of thousands of ethnic Yazidis stranded in mountains by the militants’ siege.

The President and other administration officials are using the term “genocide” when referring to the situation and is already sending supplies to help the Yazidis.

Militants raided the Yazidi town of Sinjar in northern Iraq over the weekend.

Yazidis are among Iraq’s smallest minorities. They are of Kurdish descent, and their religion is considered a pre-Islamic sect that draws from Christianity, Judaism and Zoroastrianism.

Islamic State has executed people who don’t share their fanatical interpretation of Sunni Islam and posted videos of their killings to the Internet. “Convert to Islam or die” is the Islamic State’s ultimatum given to those captured.

They have also beheaded victims and placed their heads on spikes to strike terror in the population, a senior administration official said.

Christians, Shiite Muslims and Yazidis have fled from the militants’ blood-paved path.

Multitudes of harried refugees have poured into the Kurdish region and camped in and around Irbil.

When Islamist fighters stormed Sinjar, thousands fled into the surrounding mountains.

Until Thursday they were without food and water, and some children died of thirst in the Iraqi summer heat.

Before the President’s address, two U.S. military cargo planes airdropped 5,300 gallons of water and 8,000 meals onto Mount Sinjar.

U.S. forces are standing by with plenty more food and water, a senior administration official said.

Possible strike to break siege

If militants continue to surround the mountain, they may have to reckon with U.S. intervention from the air.

“When we have the unique capabilities to help avert a massacre, then I believe the United States of America cannot turn a blind eye,” Obama said. “We can act, carefully and responsibly to prevent a potential act of genocide.”

U.S. Secretary of State John Kerry on Friday repeated the administration’s concerns about genocide.

The Islamic State’s “campaign of terror against the innocent, including the Yazidi and Christian minorities, and its grotesque targeted acts of violence show all the warning signs of genocide,” Kerry said Friday during a televised press conference in Kabul, Afghanistan. “The stakes for Iraq’s future could not be more clear,” and “for anyone who (needs) a wake-up call, this is it.”

Fear of U.S. ground troops

Obama brought home American forces from Iraq more than two years ago, and on Thursday, he addressed American concerns about boots on the ground there.

“As commander in chief, I will not allow the United States to be dragged into fighting another war in Iraq,” Obama said.

The administration has put the onus on the Iraqi government, which it has pushed to reform.

It wants Iraqi Prime Minister Nuri al-Maliki’s Shiite-dominated regime replaced by an ethnically more inclusive government.

Already, the Obama administration is rapidly funneling weapons to Iraqi forces. Factories in the United States are operating seven days a week to produce them, a senior administration official said.

But two Republican senators said in a statement that the President’s actions do not go far enough. And the United States should not wait on Iraq to pull together before Washington takes action.

Sens. John McCain of Arizona and Lindsey Graham of South Carolina want to see U.S. forces take the fight to the Islamic State.

“It should include U.S. airstrikes against ISIS leaders, forces, and positions both in Iraq and Syria,” their statement read.

Iraqi forces fight back

The Iraqi air force bombed a number of Islamic State targets Thursday night, Qubad Talabani, deputy prime minister of the Kurdish regional government, told CNN. The strikes killed at least two of the group’s emirs, he said.

The United States has been sharing intelligence through reconnaissance but is not involved in any airstrikes, a senior Iraqi military official told CNN on Thursday.

Americans “almost consistently” have manned or unmanned observation aircraft over Irbil, a senior administration official said.

The United States has 245 military personnel in Iraq, 90 of whom are advisers. The carrier USS George H.W. Bush and other Navy ships also are in the region.

The Islamic State fighters have captured armored vehicles and other military hardware from Iraqi forces in a lightning sweep through the north earlier this year.

The militant group’s name, Islamic State, reflects its goal to establish a Sunni caliphate stretching from Syria to Baghdad.

After establishing the religious state, the group envisions expanding it throughout the world.