(CNN) -- The United States launched a series of airstrikes Wednesday against ISIS forces in Iraq, the same day President Barack Obama vowed to act against the militant group following its beheading of an American journalist and its threat to kill another.

"The United States of America will continue to do what we must do to protect our people. We will be vigilant and we will be relentless," the President said in televised remarks.

Obama vowed justice for James Foley, calling his killing by ISIS, which refers to itself as the Islamic State, an act of violence that "shocked the conscience of the entire world."

The President's statement followed Tuesday's release by ISIS of a video that showed Foley's killing and carried a stark warning that a second American, believed to be journalist Steven Sotloff, would be killed, if the United States did not end its military operations in Iraq.

Whether Sotloff lives or dies, the executioner said on the video, depends on what Obama does next.

ISIS is believed to be holding a number of Americans, including Sotloff, a U.S. official told CNN. The official, who spoke on condition of anonymity, declined to say exactly how many Americans were being held or to identify them.

Also Wednesday, Pentagon spokesman Rear Adm. John Kirby said in a written statement that the United States attempted a rescue operation earlier this summer to free a number of American hostages held in Syria by ISIS.

"Unfortunately, the mission was not successful because the hostages were not present at the targeted location," he said.

Another U.S. official, speaking on condition of anonymity, told CNN that the mission was to rescue Foley and others being held at an undisclosed location.

If ISIS, also known as ISIL, hoped the execution video and threat would ease U.S. military involvement in Iraq, it failed.

Calling ISIS a "cancer," Obama said across the Middle East there has to be a common effort to put an end to the group.

"Friends and allies around the world, we share a common set of values that are rooted in the opposite of what we saw yesterday," he said. "And we will continue to confront this hateful terrorism and replace it with a sense of hope and civility."

As the President spoke, the Pentagon confirmed the United States carried out 14 airstrikes against mobile ISIS targets in the vicinity of the Mosul Dam, which Kurdish forces recaptured from the terror group with the support of American airpower.

Humanitarian operation underway

Obama ordered targeted airstrikes in Iraq this month to protect U.S. personnel and facilities, as well as minorities being brutalized by ISIS.

The campaign by ISIS in Iraq began in June when the group swept in from Syria, seizing Iraq's second-largest city of Mosul.

ISIS militants, who are Sunni Muslim extremists, have carried out brutal attacks on towns and villages as they've advanced across Iraq, targeting Iraq's Christians, minority sects such as the Yazidis, centered in the northern Sinjar area, and Shia Muslims.

The UNHCR estimates that 1.2 million Iraqis have been forced from their homes so far this year, including more than one hal million in the western Anbar province and a similar number in northern Iraq.

A plane carrying the first load of humanitarian aid as part of a multiday operation to help hundreds of thousands of displaced people in northern Iraq has landed in Irbil, the U.N. refugee agency said.

"It's the largest single aid push we have mounted in more than a decade," the U.N. High Commissioner for Refugees, Antonio Guterres, said.

The first Boeing 747 to land carried 100 tons of aid, he said. Three more flights will follow from Jordan into Irbil, the Kurdish regional capital, with the last on Saturday.

The airlift will be bolstered by deliveries made by road and sea over the next 10 days, with 175 trucks ferrying cargo from warehouses in Turkey, Jordan and Iran.

The shipments include thousands of tents, plastic sheets, kitchen sets and jerrycans, destined for families who fled with little more than the clothes on their back.

What to know about ISIS

More US troops to Iraq?

As the massive aid operation swings into gear, fierce fighting continues between the militants and Kurdish forces for control of northern Iraq.

On Tuesday, U.S. airstrikes helped Kurdish and Iraqi forces take control of the key Mosul Dam, fighting back the militants who had seized it.

The stakes were huge for the millions of Iraqis who live downstream from the dam, the largest in the country, amid fears that if it were breached floods would have threatened lives in Mosul and downriver in Baghdad.

Now that the dam is cleared of ISIS militants, Iraqi forces are moving to grow their area of control, the Defense Department said.

The Pentagon is considering a State Department request for more U.S. troops to protect U.S. government personnel in the Baghdad area, a U.S. official confirmed to CNN.

If approved, the troops would number less than 300, said the official, who spoke on condition of anonymity.

"There is a request by the State Department for additional security personnel in and around Baghdad," the official said. The official would not say where the troops would go, but there are two publicly known locations for American personnel working in Baghdad -- the U.S. Embassy and Baghdad International Airport.

The official insisted that there was no specific threat that led to this request, which Defense Secretary Chuck Hagel would have to approve.

The troops would be in addition to the hundreds of American military advisers already in the country advising Iraqi troops in their fight against ISIS.

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CNN's Barbara Starr, Jennifer Deaton and Richard Roth contributed to this report