WASHINGTON — In a horrifying act of revenge for U.S. airstrikes in northern Iraq, militants with the Islamic State extremist group have beheaded American journalist James Foley — and are threatening to kill another hostage, U.S. officials say.

The White House must now weigh the risks of adopting an aggressive policy to destroy the Islamic State against resisting any action that could result in the death of another American.

It will also confront the potentially necessary step of pursuing the Islamic State in Syria, where President Barack Obama has resisted launching airstrikes or deploying significant American firepower.

Obama was expected to make a statement Wednesday about Foley’s killing.

U.S. officials confirmed a grisly video released Tuesday showing Islamic State militants beheading Foley. Separately, Foley’s family confirmed his death in a statement posted on a Facebook page that was created to rally support for his release, saying they “have never been prouder of him.”

“He gave his life trying to expose the world to the suffering of the Syrian people,” said the statement, which was attributed to Foley’s mother, Diane Foley. She implored the militants to spare the lives of other hostages. “Like Jim, they are innocents. They have no control over American government policy in Iraq, Syria or anywhere in the world.”

Foley, 40, from Rochester, N.H., went missing in northern Syria in November 2012 while freelancing for Agence France-Presse and the Boston-based media company 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.

The beheading marks the first time the Islamic State has killed an American citizen since the Syrian conflict broke out in March 2011, upping the stakes in an increasingly chaotic and multilayered war. The killing is likely to complicate U.S. involvement in Iraq and the Obama administration’s efforts to contain the group as it expands in both Iraq and Syria.

The group is the heir apparent of the militancy known as al-Qaida in Iraq, which beheaded many of its victims, including American businessman Nicholas Berg in 2004.

The video released on websites Tuesday appears to show the increasing sophistication of the Islamic State group’s media unit and begins with scenes of Obama explaining his decision to order airstrikes.

It then cuts to a balding man in an orange jumpsuit kneeling in the desert, next to a black-clad militant with a knife to his throat. Foley’s name appears in both English and Arabic graphics on screen. After the captive speaks, the masked man is shown apparently beginning to cut at his neck; the video fades to black before the beheading is completed. The next shot appears to show the captive lying dead on the ground, his head on his body. The video appears to have been shot in an arid area; there is no vegetation to be seen and the horizon is in the distance where the sand meets the gray-blue sky.

At the end of the video, a militant shows a second man, who was identified as another American journalist, Steven Sotloff, and warns that he could be the next captive killed. Sotloff was kidnapped near the Syrian-Turkish border in August 2013; he had freelanced for Time, the National Interest and MediaLine.

One U.S. official said the video appeared to be authentic, and two officials said the victim was Foley. All three officials spoke on condition of anonymity because they were not authorized to discuss the killing by name.

Several senior U.S. officials with direct knowledge of the situation said the Islamic State very recently threatened to kill Foley to avenge the crushing airstrikes over the past two weeks against militants advancing on Mount Sinjar, the Mosul dam and the Kurdish capital of Irbil.

Both areas are in northern Iraq, which has become a key front for the Islamic State as its fighters travel to and from Syria.

Since Aug. 8, the U.S. military has struck at least 70 Islamic State targets — including security checkpoints, vehicles and weapons caches. It’s not clear how many militants have been killed in the strikes, although it’s likely that some were.

The Islamic State militant group is so ruthless in its attacks against all people they consider heretics or infidels that it has been disowned by al-Qaida’s leaders. In seeking to impose its harsh interpretation of Islamic law in the lands it is trying to control, the extremists have slain soldiers and civilians alike in horrifying ways — including mounting the decapitated heads of some of its victims on spikes.

The New York-based Committee to Protect Journalists estimated Tuesday that about 20 journalists are missing in Syria, and has not released their nationalities. In its annual report in November, the committee concluded that the missing journalists were either being held and threatened with death by extremists, or taken captive by gangs seeking ransom. The group’s report 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.