A new video purporting to show British war photographer John Cantlie has appeared online in which he mocks US President Barack Obama.
It is the first time in more than a year that Mr Cantlie, captured by Islamic State in Syria in 2012, has been seen alive.
The photojournalist, who has fronted a series of videos for IS while a hostage, appears gaunt as he ridicules US attempts to destroy the terrorist group.
His supporters swiftly dismissed the film, which is dated Saturday but has not been verified, saying: "His words are not those of a free man." They also questioned when it was made.
The Foreign Office said it was "looking at the contents of this latest propaganda video".
The clip, which first appeared on Twitter, shows the journalist clad in black as he walks around a bomb-damaged building he claims is in the northern Iraqi city of Mosul.
Filmed in daylight, Mr Cantlie is stood beside a road busy with traffic and a number of people can be seen walking by in the background.
Addressing the camera as if presenting a television programme, he says: "After 20 months and 5 billion dollars, America has successfully destroyed an Islamic State media kiosk.
"If this is what Obama meant about degrading and ultimately destroying Isis, he's clearly got a long way to go yet.
"And you know what's really just amazing, given the amount of money that America is spending on this war, it would go to the effort of destroying a small shack like this, in the middle of Mosul."
He suggests the kiosk, which cost 50 dollars (£35), to build was targeted because the US is "bankrupt of intelligence" on IS targets.
Mr Cantlie's skills as a journalist have been exploited by IS in an attempt to lend credibility to propaganda films, including a series titled Lend Me Your Ears.
The last was released in November 2014.
Journalist Hala Jaber tweeted: "Worth remembering that whatever #John_Cantlie says, he is & remains a hostage and that his words are not those of a free man."
Mr Cantlie's sister Jessica has previously appealed for "direct contact" with the militants holding him. His father Paul, 80, died from complications following pneumonia in 2014.