Cameron took to Twitter Wednesday to call the beheading "shocking and depraved."
If true, the murder of James Foley is shocking and depraved. I will today chair meetings on the situation in Iraq/Syria.— David Cameron (@David_Cameron) August 20, 2014
A statement from Cameron's office at Number 10 Downing Street said the prime minister is returning to London to host a meeting with Foreign Secretary Philip Hammond to discuss the threat of IS in Iraq and Syria. Cameron has been on holiday in southwest England.
The jihadist in the video has a British accent, but his nationality and identity have not been verified. Hammond told BBC radio a number of British nationals have gone to Syria to fight for IS.
"Now we will have to do some more analysis to make quite certain that that is the case, but we've been saying for a very long time that there are significant numbers of British nationals in Syria and increasingly in Iraq," he said.
U.S. President Barack Obama has been briefed on the video and will "receive regular updates," said White House spokesman Eric Schultz. The president is scheduled to make a statement on the video from Martha's Vineyard at 12:45 p.m. Wednesday.
"We have seen a video that purports to be the murder of U.S. citizen James Foley by (ISIS)," said National Security Council spokeswoman Caitlin Hayden. "The intelligence community is working as quickly as possible to determine its authenticity. 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. We will provide more information when it is available."