In brief but forceful remarks, Obama said the U.S. would "do what we must to protect our people," but he stopped short of promising to follow the Islamic State in its safe haven within Syria, where officials said Foley had been killed. Later, though, the administration revealed that several dozen special operations troops had been on the ground in Syria briefly in an effort to rescue the hostages, but did not find them.
And looking forward, the State Department refused to rule out future U.S. military operations in Syria, where Obama has long resisted intervening in a three-year civil war.
Western nations agreed to speed help to combat the militants — most notably Germany, which bucked public opposition by announcing it would arm Iraqi Kurdish fighters to battle the Islamic State. French Foreign Minister Laurent Fabius said he was outraged by the beheading, deeming it evidence of a "caliphate of barbarism." Italy's defense minister said the country hopes to contribute machine guns, ammunition and anti-tank rockets.
The Islamic State called Foley's death a revenge killing for U.S. airstrikes against militants in Iraq, and said other hostages would be slain if the attacks continued. Undeterred, the U.S. conducted 14 additional strikes after a video of the beheading surfaced, bringing to 84 the number of airstrikes since they began on Aug. 8.
Two U.S. officials said additional American troops — probably less than 300 — could be headed to Iraq to provide extra security around Baghdad, where the U.S. Embassy is located. That would bring the total number of American forces in Iraq to well over 1,000, although officials said no final decision had been made. The officials spoke on condition of anonymity because they were not authorized to discuss the matter by name.
Foley's mother said she is praying for other hostages being held by the Sunni-dominated terror group, and described her son's slaying as "just evil."
"No just God would stand for what they did yesterday, and for what they do every single day," the president said. The Islamic State militants have promised to eliminate all people they consider heretics in their quest to create an extremist state across much of Iraq and Syria.
"We will be vigilant and we will be relentless," Obama said, urging unity among Mideast governments in order to eviscerate the extremist group's growing power. He spoke from Martha's Vineyard in Massachusetts, where his family is vacationing.
In capitals across the Middle East, news of Foley's death was met largely with silence, even in Syria and Iraq — the two countries where the Islamic State is strongest. On social media, people in the region condemned Foley's killing, but stressed that the Islamic State has been committing atrocities against Iraqis and Syrians for years.
For much of the past year, and until this summer, the Obama administration was deeply divided on how much of a threat the Islamic State posed to Americans or even other nations beyond Iraq and Syria. But since the militants' march across northern Iraq in June, and as its ranks swelled almost threefold to an estimated 15,000 fighters, Obama has acknowledged that the Islamic State could become a direct threat to Americans.
The secret mission to rescue the U.S. hostages involved several dozen special operations forces dropped by aircraft into Syria. The hostages weren't found, but special forces engaged in a firefight with Islamic State militants before departing, according to administration officials. Several militants were killed, and one American sustained minor injuries.
"The U.S. government had what we believed was sufficient intelligence, and when the opportunity presented itself, the president authorized the Department of Defense to move aggressively to recover our citizens," Lisa Monaco, Obama's top counterterrorism adviser, said in a statement. "Unfortunately, that mission was ultimately not successful because the hostages were not present."
Foley's death proved to the West what many people in Syria and Iraq already knew: The Islamic State "has declared war on the civilized world," said Dr. Najib Ghadibian, the Syrian National Coalition's special representative to the U.S. The group's sweep also has served as a wake-up call to other Mideast governments, said Fawaz Gerges, director of the Middle East Center at the London School of Economics.
"The Saudis, the Kuwaitis, the Emiratis, and even the Qataris, are getting the message now," Gerges said. "I think in the last few weeks we have seen a kind of new awareness on the part of regional powers that the Islamic State does present a threat to the very social fabric and the foundation of the state system."
He said Foley's death could help intensify efforts on the part of Washington's regional allies to make a more concerted effort to address the threat.
Jordan and Saudi Arabia, both of whom share a border with Iraq, have dispatched troops to the frontier in a bid to prevent any attempt by the extremists to attack. Iran, an ally of the Shiite-led government in Baghdad, has sent military advisers to help organize Shiite militias in Iraq and defend holy sites.
Authorities from the Gulf to Egypt, as well as their peoples, have looked on with growing concern as the Islamic State group has brutally expanded the territory under its control, punctuating its rise by declaring a caliphate in lands straddling the Syria-Iraq border.
Foley, a 40-year-old journalist from Rochester, New Hampshire, was no stranger to war zone reporting. He went missing in northern Syria in November 2012 while freelancing for Agence France-Presse and the Boston-based news organization GlobalPost. The car he was riding in was stopped by four militants in a contested battle zone that both Sunni rebel fighters and government forces were trying to control. He had not been heard from since.
He was one of at least four Americans still being held in Syria — three of whom officials said were kidnapped by the Islamic State. The fourth, freelance journalist Austin Tice, disappeared in Syria in August 2012 and is believed to be in the custody of government forces in Syria.
The Islamic State video of Foley's beheading also showed another of the missing American journalists, Steven Sotloff, and warned he would be the next killed if U.S. airstrikes continued. U.S. officials believe the video was made days before its Tuesday release, perhaps last weekend, and have grown increasingly worried about Sotloff's fate.
The New York-based Committee to Protect Journalists says that more than 80 journalists have been abducted in Syria, and estimates that around 20 are currently missing there. It has not released their nationalities. In its annual report in November, the committee described the widespread seizure of journalists as unprecedented and largely unreported by news organizations in the hope that keeping the kidnappings out of public view may help in the captives' release.
Obama avoided specific mention of the other American hostages in Syria, and was vague on whether the U.S. would significantly ramp up its assault on the Islamic State beyond the airstrikes and small potential increase in troops in Iraq. A third senior U.S. official said the administration was well aware of the risks to the hostages once the strikes began, and would now consider as aggressive a policy as possible to obliterate the militants.
At the State Department, spokeswoman Marie Harf did not rule out military operations in Syria to bring those responsible to justice, saying the U.S. "reserves the right to hold people accountable when they harm Americans."
U.S. lawmakers, however, said they doubted the White House would expand its attacks to strike within Syria — something the Obama administration has long resisted.
"The mission already crept a bit," said Rep. Adam Schiff, a California Democrat and House Intelligence Committee member. "The administration would be wise to not get sucked in. That's going to be very hard."
Sen. Marco Rubio, R-Fla., lamented that Obama has been "unwilling to do what is necessary to confront" the Islamic State.
Lucas reported from Beirut. Associated Press writers Lolita C. Baldor, Bradley Klapper, and Josh Lederman in Washington, Jim Kuhnhenn in Massachusetts, Rik Stevens in Rochester, New Hampshire, and Zeina Karam in Beirut contributed to this report.
Crisis in Iraq