As calls mounted for Washington to expand its military intervention against the Islamic State (IS) jihadist group, it also threatened to kill another US reporter if the strikes did not stop.
The video posted online yesterday showed a masked militant beheading a man resembling James Foley, who has been missing since he was seized in Syria in November 2012.
News of Foley's apparent beheading comes as US air strikes appeared to yield some results, helping Kurdish and federal forces push IS fighters back from some recently-conquered areas in northern Iraq, including the strategic Mosul dam.
"We have never been prouder of our son Jim. He gave his life trying to expose the world to the suffering of the Syrian people," Foley's mother Diane said in a Facebook message to supporters.
More From This Section
"We implore the kidnappers to spare the lives of the remaining hostages. Like Jim, they are innocents. They have no control over American government policy in Iraq, Syria or anywhere in the world."
The White House said US intelligence was studying the video, and that President Barack Obama had been briefed on it as he flew from Washington to resume his vacation on Martha's Vineyard.