David Cameron has warned the West must act "carefully and methodically" to deal with the threat of Islamic State amid a growing clamour for Britain to join US air strikes against the terrorists controlling large swathes of Iraq and Syria.
At the Nato summit in Wales, the Prime Minister insisted that Britain was not yet at the stage where it was ready to take offensive military action and called for a "comprehensive plan" involving nations in the region.
Earlier, US secretary of state John Kerry appeared to try to up the tempo, calling for agreement on an international plan for dealing with IS by the time of the general meeting United Nations General Assembly in New York later this month.
Mr Kerry and Foreign Secretary Philip Hammond jointly chaired a meeting of foreign and defence ministers from what the US called a "core coalition" of allies to discuss the way forward.
Ministers from France, Australia, Germany, Canada, Turkey, Italy, Poland and Denmark were also at the talks.
"We have the technology, we have the know-how. What we need is obviously the willpower to make sure that we are steady and stay at this," Mr Kerry said. "We need to have this coalesce."
There was some irritation among British officials at the apparent attempt to put a group of predominantly North American and European nations at the forefront of the effort at a time when they are seeking to build support from allies in the region.
At his end of summit press conference, Mr Cameron said: "My argument is you need that mixture of intelligent politics, diplomatic pressure, long-term engagement in a comprehensive plan as well as the potential for military or other more aggressive action.
"This will take time and it will take resolve. We will proceed carefully and methodically, drawing together the partners we need, above all in the region, to implement a comprehensive plan."
Earlier Mr Hammond said the Government will not be deterred from launching air strikes against IS by threats to the life of a British hostage they are holding.
IS militants - also referred to as Isil or Isis - have threatened to kill Scottish aid worker David Haines who they are believed to be holding in Syria.
They have already beheaded two American journalists, posting the evidence on line in gruesome videos featuring a masked jihadist with a British accent.
"We will do everything we can to protect this individual (Mr Haines) but we have to be clear about the nature of the organisation that we are dealing with," Mr Hammond told BBC News.
"They are utterly brutal, they are ideologically driven - almost pathological in the way that they behave. We cannot allow our strategy to be driven by their behaviour.
"We have to approach the challenge of Isil with focus purely on what is in Britain's best interests - protecting our citizens and our security from the threat that Isil poses from foreign fighters, from potential attacks on our soil, destabilisation of the region.
"We will not be diverted from doing what is right by the threats from this organisation."
Mr Haines, 44, has a teenage daughter in Scotland from a previous marriage and a four-year-old daughter in Croatia from his present marriage.
Educated at Perth Academy secondary school, he has 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.
He spoke to MediaGlobal News while there about work he and his team were doing to prevent children being killed or maimed playing with unexploded ordnance like mortars and cluster bombs
"Only two and a half weeks ago in Ajdabiya a child took one of these items home, and unfortunately the father decided to have a look at it and it exploded," he told the site.
Speaking to the Daily Telegraph at the family's home near Zagreb, his wife Dragana Prodanovic Haines, 44, said: "He's everything to us. He's our life. He's a fantastic man and father.
"Nobody can understand how we are feeling. My daughter keeps asking about him every day. She hasn't seen her father for a year and a half. She has gone through so much. She sees me crying all the time."
His brother Michael was quoted telling reporters: "We do not want to answer any questions but we acknowledge that you are being tactful and careful with your approach."
Defence Secretary Michael Fallon said the struggle against the Islamic State would take "months and possibly years" and could not be resolved simply by swift air strikes.
Asked how Britain would respond to a request for air strikes against IS forces from the new Iraqi government expected to be formed in the next few days, Mr Fallon told BBC News: "Each country will have to respond and parliaments across Nato will have to come to their own decisions as to whether they are prepared to get behind military action to halt the advance of Isil.
"Air strikes alone aren't going to defeat Isil. This has to be done on a much broader scale, it has to involve all of us in the alliance standing together, it has to involve other countries in the Middle East, and it's an engagement that is going to take months and possibly years.
"So it's not simply a question of air strikes."
Mr Fallon added: "What has really impressed me about this summit has been the cohesion, the understanding, that there is a threat now to almost all of us from the rise of Islamic extremism in the Middle East.
"We have all now come together on the understanding that we have got to help the new government in Iraq and we've got to help moderate opinion in the Middle East mobilise and halt the advance of Isil and start to drive it back. We are willing to help in that."
The charity which employs Mr Haines said he had worked as "a humanitarian" since 1999, helping people in the Balkans, the Middle East and Africa.
When he was taken by jihadis in Syria he was working to help "tens of thousands of people affected by the crisis" created by the long-running civil war, said ACTED.
The charity said that the threats made to the Scotsman's life were "intolerable" and called for his immediate release.
US president Barack Obama said Nato members were "unanimous" in their commitment to stamp out to the "extremist nihilism" of ISIL.
Speaking to reporters at a Nato Summit press conference, he said: "We are going to achieve our goal. We are going to degrade and ultimately defeat ISIL, the same way that we have gone after al Qaida.
"You initially push them back, you systematically degrade their capabilities, you narrow their scope of action, you slowly shrink the space, the territory that they may control, you take out their leadership, and over time they are not able to conduct the same kinds of terrorist attacks as they once could."
He welcomed the news US forces had killed the co-founder of Somalia's al-Shabaab Islamist group, Ahmed Godane, in an air strike.
He added: "We have been very systematic and methodical in going after these kind of organisations".