Four Lions follows four Sheffield men who conspire to kill thousands at the London Marathon
A British comedy about a group of aspiring suicide bombers has premiered at the Sundance Film Festival.
Four Lions was created by satirist Chris Morris, who was behind the controversial Channel 4 show Brass Eye.
He said the film shows "the Dad's Army side to terrorism", as four incompetent jihadists plan to attack London.
Early reviews described the movie as "deliciously subversive", but suggested that a shift in tone from satire to thriller in the second half fell flat.
"As a satire on terror, Four Lions seems to be a missed opportunity precisely because of those tonal shifts," wrote Jeremy Kay in The Guardian.
Film magazine Empire was more positive, noting that the movie "articulates an inclusive viewpoint" in which the "notion of 'them and us' does not just boil down to race: It boils down to them, the idiots, and us, the people who only see horror in extremism".
Arsher Ali, who plays one of the would-be terrorists, told the BBC that the film is first and foremost, a comedy.
"It's a dynamic of a bunch of guys who get together and mess everything up," he told Radio 4's Today programme.
"Terrorism is in the news almost every day, but there are little stories within those things that are inherently comic and inherently human.
"A film like this is obviously a very strong counterpoint to the very serious side of it, which none of us condone, but there are human stories that need to be told, which can be quite touching."
But the British-funded film is guaranteed to cause controversy, according to David D'Arcy from Hollywood trade publication Screen International.
"It will offend all sorts of people," he said. "It will offend the British, it will offend Muslims, it will offend jihadists.
"But if satire doesn't offend people, it is not satire."
Morris has refused requests for interviews, but addressed the Sundance audience following the premiere, telling them the film was inspired by an account of a botched terror attack he read five years ago.
"It was like an Ealing comedy," he said. "I felt there was a missing link and these guys were pretty foolish."
Chris Morris was behind TV shows The Day Today and Brass Eye
Four Lions is just one of several films at Sundance to touch on contentious contemporary political and social issues.
One documentary looks at the Mormon church's influence on the 2008 ballot which banned gay marriage in California, and many other dramas are set against the backdrop of the conflicts in Iraq and Afghanistan.
One of them, Buried, became the first movie to find a buyer at the festival.
Starring Ryan Reynolds, it is a claustrophobic thriller about a civilian truck driver trapped in a coffin in Iraq. The film takes place almost entirely underground.
Film studio Lionsgate snapped up the rights to the movie for $3.2m (£1.98m) after it screened to near-universal approval on Sunday.
The Sundance festival runs until 31 January in Utah.
A total of 113 movies from the US and around the world are screened at the annual event, organised by film star Robert Redford.