David Haines: PM says Britain will 'hunt down' IS killers

Mr Haines was kidnapped last year a few days after arriving in Syria to deliver aid

David Cameron says Britain will hunt down those responsible for the death of British aid worker David Haines.

Speaking after a Cobra meeting, the prime minister paid tribute to the 44-year-old "British hero" who was held hostage and killed by Islamic State [IS] militants.

He also said the country was "sickened" that a Briton could have carried out the "despicable" killing.

IS militants "are not Muslims, they are monsters," Mr Cameron said.

Mr Haines was seized in Syria in 2013. He was being held by Islamic State militants who had already killed two US captives.

A video of the aid worker's beheading was released on Saturday night. The video begins with a clip of Mr Cameron and then features a man who appears to be Mr Haines dressed in orange overalls, kneeling in front of a masked man holding a knife.

The victim says: "My name is David Cawthorne Haines. I would like to declare that I hold you, David Cameron, entirely responsible for my execution."

He says Mr Cameron had entered into a coalition with the US against the Islamic State "just as your predecessor Tony Blair did".

"Unfortunately it is we the British public that in the end will pay the price for our parliament's selfish decisions," he said.

The militant, who appears to have a British accent, is then recorded as saying: "This British man has to pay the price for your promise, Cameron, to arm the Peshmerga against the Islamic State."

The Foreign Office says the video appears to be genuine.