Islamic State video purports to show Paris attackers, threatens Britain

Reuters could not independently verify the authenticity of the footage, which showed the men delivering anti-Western diatribes and concluded with an apparent threat to attack Britain.

The French Foreign Ministry declined to comment on the video. There was no immediate comment from the prime minister's office, and Reuters was not immediately able to reach officials at the Interior Ministry.

A spokeswoman for the National Security Council at the White House had no comment.

Laith Alkhouri of Flashpoint Global Partners, which monitors militants' social media, said the "video meets all the right criteria of an authentic and official ISIS release."

The video was uploaded to Islamic State's official Telegram channel and showed some of the attackers wearing camouflage fatigues in a desert location, before the time of the Paris attacks.

Several of them were shown beheading hostages of the ultra-hardline militant group, a tactic it has frequently used.

"These are the last messages of the nine lions of the caliphate who were mobilized from their lairs to make a whole country, France, get down on its knees," a narrator in the video said.

On the night of Nov. 13, nine men, split into three groups, attacked a sports stadium, a string of cafes and a concert hall. An arrest warrant has been issued for another man, Salah Abdeslam, who fled to Belgium the following day.

The attackers are identified in the video by noms de guerre referring to their nationalities - three French, four Belgian and two Iraqis, referred to as Ali al-Iraqi and Ukashah al-Iraqi.

The two could be the suicide bombers who tried to attack the Stade de France stadium. They carried Syrian passports assumed to be forged and could not be formally identified. Seven other dead attackers have already been identified.

The video showed footage of British Prime Minister David Cameron expressing solidarity with the French people after the attacks, and concluded by flashing a slogan on the screen saying: "Whoever stands in the ranks of kafir (infidels) will be a target for our swords."

A spokesman for Cameron had no immediate comment.

(Reporting by Eric Knecht and Matthias Blamont; Additional reporting by Mark Hosenball in Washigton and William Schomberg in London; Writing by Mark Trevelyan; Editing by David Clarke, Mary Milliken and Peter Cooney)