U.S. intelligence analysts have determined that the video showing the beheading of American photojournalist James Foley by Islamic State militants is real, officials said Wednesday.
"We have reached the judgment that this video is authentic," National Security Council spokeswoman Caitlin Hayden said.
The "entire world is appalled" and the nation "heartbroken," said President Obama, speaking Wednesday from his vacation on Martha's Vineyard in Massachusetts. The White House declined to comment on reports that officials knew of specific threats to Foley's life before the beheading video was posted online Tuesday.
Obama accused the Islamic State of torture, rape and murder, saying the militants speak for no religion and terrorize their neighbors.
"Their victims are overwhelmingly Muslim," he said. "Their ideology is bankrupt."
The future, Obama said, is shaped by people like Foley, who was covering the Syrian civil war when he was kidnapped in 2012. The president urged Muslim nations to band together to stop IS, which is waging a war aimed at building an arch-conservative Sunni state across a swath of Syria and Iraq.
"We will continue to confront this hateful terrorism and replace it with a sense of hope," Obama vowed.
Obama made no mention of missing U.S. journalist Steven Joel Sotloff, who is shown alive in the Islamic State video titled "A Message to America." In the video, a man wearing a black hood says Foley's beheading is a revenge killing for U.S. airstrikes in Iraq.
"Any attempt by you, Obama, to deny the Muslims their right to live in safety under the Islamic caliphate will result in the bloodshed of your people," the hooded man says in a British accent with Foley kneeling beside him. Foley, 40, delivers what appears to be a scripted statement in which he asserts that U.S. airstrikes on Islamic State militants in Iraq "signed my death warrant."
After the beheading, the killer warns Obama that Sotloff's life "depends on your next decision."
Foley, a New Hampshire native, worked for several years as a video journalist in the Middle East. He covered wars in Iraq and Afghanistan and, in 2011, was among four journalists detained by the Libyan military. Foley was freed after 44 days.
Foley's parents held a press conference Wednesday, saying they had spoken briefly with Obama. The couple thanked supporters for their prayers and lauded their son's resolve.
"So many people were praying for him, and I really think that gave him unusual courage," said Foley's mother, Diane Foley. "Jim had big heart — that's what we shared with President Obama. We pray that Jim's death can bring our country together in a strong way with the values Jim held dear. Jim would never want us to hate or be bitter.
"We are just very proud of Jimmy."
Secretary of State John Kerry said in a statement that he was a senator when he first met Foley's parents during their son's captivity in Libya.
"We grieve for James Foley. We mourn for his family and his loved ones," Kerry said in the statement. "We honor the courage and pray for the safety of all those who risk their lives to discover the truth where it is needed most. And make no mistake: We will continue to confront (the Islamic State) wherever it tries to spread its despicable hatred."
In 2002, Wall Street Journal reporter Daniel Pearl was abducted in Pakistan by British national Ahmed Omar Saeed Sheikh. Pearl was later slain by his captors in Pakistan.
"Our hearts go out to the family of journalist James Foley. We know the horror they are going through." Pearl's mother, Ruth, said in a tweet from the Daniel Pearl Foundation.
British Prime Minister David Cameron's called Foley's murder "depraved." Cameron's office said he was cutting short his vacation and returning to the capital to discuss the situation in Iraq and Syria and the threats posed by IS.
The United Kingdom's Foreign Secretary Philip Hammond said Foley's beheading may have been undertaken by a British national.
In an interview with the BBC, Hammond acknowledged that the militant shown in the video with Foley spoke with a British accent. It's possible that the perpetrator of the shocking killing could be British, he said.
"We're absolutely aware that there are significant numbers of British nationals involved in terrible crimes, probably in the commission of atrocities, making jihad with IS and other extremists organizations," Hammond told the BBC.
"This is something we have been tracking and dealing with for many, many months and I don't think this video changes anything," he said. "It just heightens awareness of a situation which is very grave."
The Islamic State "is clearly sending a message to the U.S. government with this act, but it's also sending a message to the American people," said Raffaello Pantucci, a researcher at Royal United Services Institute in London, a security think tank. "The American public will look at this and think: 'What is Obama doing (in Iraq)?'"
Contributing: Donna Leinwand Leger