Muslim communities in Britain have condemned the killing of British aid worker David Haines in Syria by Islamic State militants.

The Imam Sayed Ali Abbas Razawi says IS does not represent his views - or that of other Muslims in Britain.

The Archbishop of Canterbury says he was killed "in the depths of evil", while the British Prime Minister David Cameron has branded Mr Haines' captors 'monsters, not Muslims'.

Speaking from Downing Street after chairing a meeting with members of the military, the security services, the Foreign Office and the Home Office, Mr Cameron described Islamic State extremists as "monsters" who are part of a "fanatical organisation".

"We will hunt down those responsible and bring them to justice, no matter how long it takes," Mr Cameron said.

"David Haines was an aid worker. He went into harm's way, not to harm people but to help his fellow human beings in the hour of their direst need, from the Balkans to the Middle East.

"David Haines was a British hero. The fact that an aid worker was taken, held and brutally murdered at the hand of Islamic State sums up what this organisation stands for. They boast of their brutality. They claim to do this in the name of Islam. That is nonsense - Islam is a religion of peace."

UK Government sources say the death will not change Britain's policy and Parliament will not be recalled. However Mr Cameron said Britain's security depends upon taking action against to fight the extremists.

"It must strengthen our resolve. We must recognise that it will take time to eradicate a threat like this. It will require, as I have described, action at home and abroad," he said.

Capture

It is 18 months since David Haines was captured in Syria, and his brother says he will ll be "missed terribly". The release of the video came only hours after Mr Haines' family urged his captors to contact them.

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

44-year-old and father of two Haines was first recorded during the execution of US journalist Steven Sotloff by the Islamic State fighters earlier this month.

In that video the aid worker was named as the next target for execution. 

The footage of Mr Haines' death shows a knife-wielding militant who speaks with a British accent.

The clip also includes a threat against a second hostage currently being held by militants. He has been named this afternoon as another aid worker - 47-year-old Alan Henning.

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

Originally published 12:14am