(Reuters) - The mother of American journalist James Foley, who was purportedly beheaded by Islamic militants, said on Tuesday her son gave his life to expose the suffering of the Syrian people and she asked his kidnappers to release their other captives.
"He was an extraordinary son, brother, journalist and person," Diane Foley said in a post on a website set up by the Foley family.
James Foley was abducted in Syria in November 2012 while reporting on the conflict there for GlobalPost.
A video released on Tuesday by Islamic State, an al-Qaeda offshoot that has overrun large swathes of northern Iraq and Syria, appeared to show Foley being beheaded.
The Sunni militants also threatened to kill another American journalist, Steven Sotloff, who went missing in Syria in July 2013, unless the United States stops its airstrikes against the group.
"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," Diane Foley said in the statement.
"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," she said.
The White House National Security Council said U.S. intelligence agencies were working to determine the authenticity of the video.
"If genuine, we are appalled by the brutal murder of an innocent American journalist and we express our deepest condolences to his family and friends," NSC spokeswoman Caitlin Hayden said in a statement.
The White House said President Barack Obama had been briefed about the video by his deputy national security adviser, Ben Rhodes.
James Foley's friends said he was an intrepid journalist who knew the dangers he faced. In 2011, he was held in Libya for 45 days by forces loyal to former Libyan leader Muammar Gaddafi.
"James was a hard-working and gutsy journalist who charged headfirst into dangerous situations in order to get the story. My heart breaks for his family," said reporter Carmen Gentile, who met Foley in 2012 when they both attended a medical training for freelance journalists working in war zones.
On Twitter, hundreds of users urged the public to neither watch nor share the video.
"All distributing James Foley lifeless body accomplishes is helping ISIS promote itself, helping them spread their terror beyond Iraq," Washington-based foreign policy expert Joshua Foust tweeted.
U.S. Representative Adam Schiff of California said the video "adds to the appalling parade of horrors perpetrated" by the Islamic State militants who have declared a caliphate in parts of Iraq and Syria they control.
"Seldom is the descriptor 'evil' applied with perfect accuracy as it is with this monstrous group that glories in death," Schiff said in a statement.
(Reporting by Eric Beech in Washington and Victoria Cavaliere in Seattle; Editing by Ken Wills)