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

David Cameron: "They are not Muslims, they are monsters"

Britain will take "whatever steps are necessary" to keep the country safe, following the killing of hostage David Haines by Islamic State militants, the prime minister has said.

David Cameron said the UK would "hunt down" the killers of the aid worker, whom he called a "British hero".

He said Britain had to confront and "ultimately destroy" the "menace" of IS in a "calm, deliberate" way.

The militants "are not Muslims, they are monsters", he added.

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 44-year-old's beheading was released on Saturday night. A masked militant who appears to have a British accent was pictured beside Mr Haines holding a knife.

'Despicable' killing

Speaking after a meeting of the UK emergency committee Cobra, Mr Cameron said: "We will do everything in our power to hunt down these murderers and ensure they face justice, however long it takes."

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

"We cannot just walk on by if we are to keep this country safe," he said.

"Step by step, we must drive back, dismantle and ultimately destroy Isil and what it stands for.

"We will not do so on our own, but with working with our allies, not just in the United States and in Europe, but also in the region."

He said the organisation posed a "massive threat" to the entire Middle East and said it would be defeated through a "comprehensive and sustained counter-terrorism strategy".

He added: "This is not about British combat troops on the ground. It is about working with others to extinguish this terrorist threat."