13/09/2014 23:19 BST | Updated 15/09/2014 17:59 BST

Tributes Paid To 'Beheaded' British Aid Worker David Haines

The brother of British aid worker David Haines, who was beheaded by Islamic militants, has paid tribute to him after a video of his murder surfaced online. Mike Haines, speaking in statement issued by the Foreign Office, said his brother had been murdered "in cold blood".

Earlier Prime Minister David Cameron described the beheading of the aid worker as "an act of pure evil" after Islamic State (IS) released a graphic video showing the 44-year-old being murdered by a militant with a knife. Mr Haines was taken hostage in Syria while working for ACTED in March last year and his brother said he had a passion for humanitarian work.

"David was most alive and enthusiastic in his humanitarian roles," he said. "His joy and anticipation for the work he went to do in Syria is for myself and family the most important element of this whole sad affair. He was and is loved by all his family and will be missed terribly."

The prime minister will gather senior representatives of the military and security services and the Foreign Office and Home Office in Whitehall at 10am to discuss the situation, a Number 10 spokesman said.

In separate statements, both David Cameron and US president Barack Obama have condemned the killing and vowed to bring the perpetrators to justice. The Prime Minister said: "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."

And Mr Obama, who recently announced moves to target IS in Syria, said: "The United States strongly condemns the barbaric murder of UK citizen David Haines by the terrorist group Isil (IS). 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.

"We will work with the United Kingdom and a broad coalition of nations from the region and around the world to bring the perpetrators of this outrageous act to justice, and to degrade and destroy this threat to the people of our countries, the region and the world."

Mr Cameron returned to Downing Street shortly after midnight and will chair a meeting of the Government's emergency Cobra committee later this morning.

The news came hours after the family of Mr Haines issued a plea to his captors to contact them. The video begins with an interview clip of the Prime Minister and then features Mr Haines dressed in orange overalls and kneeling down in front of a man holding a knife in what appears to be a desert location.

The victim looks into the camera and says: "My name is David Cawthorne Haines. I would like to declare that I hold you David Cameron entirely responsible for my execution. 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 militant, who appears to have a British accent, then says: "This British man has to the 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 and playing the role of the obedient lapdog Cameron, will only drag you and your people into another bloody and unwinnable war", he continues.

The video then shows the man take a knife to Mr Haines' throat, before the victim's dead body is shown. The militant adds: "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."

Militants from Islamic State previously beheaded two American journalists, posting the evidence online in gruesome videos featuring a masked jihadist with a British accent.

The Foreign Office said Mr Haines's family had asked for privacy. A spokeswoman said: "If true this is another disgusting murder. We are offering the family the family every support possible." In his tribute, Mike Haines added the father-of-two was "brought up to know right from wrong".

He said: "David was like so very many of us, just another bloke. Born in 1970 to parents who loved us both, our childhood was centred around our family. Holidays in caravans and tents, days away as a family which we remember fondly. David and I were brought up to know right from wrong, although we might not with the innocence of youth have always chosen right. David was a good brother, there when I needed him and absent when I didn't. I hope that he felt the same way about me.

WARNING: Disturbing image below

"He was, in the right mood, the life and soul of the party and on other times the most stubborn irritating pain in the ass. He would probably say the same about me. After leaving school he worked with the Royal Mail before joining the RAF as an aircraft engineer. He married his childhood sweetheart Louise and in the due process of time had a wee lass Bethany. He was - and no doubt wherever he is - exceptionally proud of Bethany.

"David served with the UN in the Balkans, helping people in real need. There are many accolades from people in that region that David helped. He helped whoever needed help, regardless of race, creed or religion. During this time David began to decide that humanitarian work was the field he wanted to work in.

Mr Haines had a teenage daughter in Scotland from a previous marriage and a four-year-old daughter, Athea, in Croatia from his present marriage. Educated at Perth Academy secondary school, he worked for aid agencies in some of the world's worst trouble spots, including Libya and South Sudan.

He was in Libya during its civil war in 2011, working as head of mission for Handicap International, which helps disabled people in poverty and conflict zones around the world. Mr Haines was taken hostage while working for ACTED in Syria in March 2013, having previously helped people in Libya and South Sudan.

ACTED previously said Mr Haines had worked as "a humanitarian" since 1999, helping people in the Balkans, the Middle East and Africa. When he was taken by jihadists in Syria he was working to help "tens of thousands of people affected by the crisis" created by the long-running civil war.

Labour leader Ed Miliband also condemned the killing, saying: "I am sickened at the disgusting, barbaric killing of David Haines. He was somebody whose only purpose was to help innocent people, themselves victims of conflict. That Isil (IS) would choose to kill him says everything about their warped logic and murderous ways.

"Acts like this will not weaken but strengthen the resolve of Britain and the international community to defeat Isil and their ideology. My deepest condolences and thoughts are with his family as they cope with this terrible crime. And the hearts of the British people will go out to them."

First Minister of Scotland Alex Salmond said the release of the video "has demonstrated a degree of brutality which defies description. It should be remembered that Mr Haines was in the region as an aid worker helping local people. His murder will be totally condemned by all people with any sense of humanity," he said in a statement. "Our thoughts, sympathies and prayers are with the family members and friends of Mr Haines who have demonstrated both dignity and courage over the past months."

Colonel Richard Kemp, former commander of British forces in Afghanistan, said: "Having worked in British Government on hostage rescue I know how much effort has gone in to saving David Haines. Now is the time for retribution." Former head of the Army Lord Dannatt said the UK should respond by playing its role in the assault against IS promised by US president Barack Obama.

"What we absolutely need to do is not be cowed in any way by yet another foul murder of a hostage," he told Sky News. "But to develop the strategy into a sensible military campaign in coalition with regional players such as Saudi Arabia, Jordan and other countries in the area. We can support them to confront, attack and defeat the Islamic State jihadi fighters ... and make sure this cancer is removed from the region before it spreads more widely."