British aid worker David Haines Killed by MILITANT

David Cameron has condemned the beheading of British aid worker David Haines by Islamic State, describing it as an "act of pure evil".

A video released by the militant organisation appears to show 44-year-old father of two Mr Haines being murdered.

In a statement put out by Downing Street, Mr Cameron says: "This is a despicable and appalling murder of an innocent aid worker. It is an act of pure evil.

"My heart goes out to the family of David Haines who have shown extraordinary courage and fortitude throughout this ordeal.

"We will do everything in our power to hunt down these murderers and ensure they face justice, however long it takes."

Mr Haines' brother Mike said his sibling was "just another bloke" who "helped whoever needed help" until he was murdered "in cold blood".

Mr Haines was thought have been held captive by militant group Islamic State after being kidnapped from a Syrian refugee camp near the border with Turkey last year.

Mr Cameron has returned to Downing Street and will chair a Cobra meeting today, officials confirmed.

The release of the video came hours after Mr Haines' family urged his captors to contact them.

In the video, the victim looks into the camera and makes a statement, holding Mr Cameron responsible for his own "execution".

In the statement, which appears to have been made under duress, he said: "You entered voluntarily into a coalition with the United States against the Islamic State just as your predecessor Tony Blair did, following a trend against our British prime ministers who can't find the courage to say 'no' to the Americans.

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

The killing comes just weeks after American journalists James Foley and Steven Sotloff were beheaded by Islamic State (IS). Those deaths were also filmed, and the videos were released on the internet.

In the new video, a man dressed in black stood behind Mr Haines. The man seemed to speak with an English accent.

After Mr Haines finished his statement, the man said: "This British man has to pay the price for your promise, Cameron, to arm the peshmerga against the Islamic State.

"Your evil alliance with America which continues to strike the Muslims of Iraq and most recently bombed the Haditha Dam will only accelerate your destruction."

"If you, Cameron, persist in fighting the Islamic State then you like your master Obama will have the blood of your people on your hands."

nother man who Sky News is not naming, said to be British, then appears at the end of the video and is threatened with being killed.

The Foreign Office said Mr Haines' family wished to be left alone.

US President Barack Obama has put out a statement saying: "Our hearts go out to the family of Mr Haines and to the people of the United Kingdom.

"The United States stands shoulder to shoulder tonight with our close friend and ally in grief and resolve."

The murders have prompted a number of commentators to call for swift and firm action. Former head of the Army Lord Dannatt said the UK should respond by playing its role in the assault against IS promised by Mr Obama.

"What we absolutely need to do is not be cowed in any way by yet another foul murder of a hostage," he said.