US secretary of state John Kerry rules out committing 'boots on the ground' at meeting of 10 nations on sidelines of Nato summit

Barack Obama has called Islamic State (Isis) a "savage organisation" that must be destroyed as the US announced the formation of a "core coalition" to combat militants in Iraq, but warned it might take two or three years to squeeze the jihadis from the region.

Speaking at the Nato summit in Wales, the US president said the organisation's members unanimously agreed on the need for immediate action against Isis militants because they pose a threat to members of the alliance.

The US secretary of state, John Kerry, said a new 10-nation grouping would concentrate on strengthening the forces in Iraq who were fighting against Isis, but said intervention would not extend to western powers sending in troops.

"We need to attack them in ways that prevent them from taking over territory, to bolster the Iraqi security forces and others in the region who are prepared to take them on, without committing troops of our own," Kerry said. "Obviously I think that's a red line for everybody here: no boots on the ground."

He said the grouping should come up with firm plans - and greater support from regional powers - by the time the UN general assembly meets for its annual session later this month. The 10 nations are the US, Britain, France, Germany, Canada, Australia, Turkey, Italy, Poland and Denmark. Significantly, the group does not include any Arab nation and only one of Iraq's six neighbours.

Obama said the international coalition needed to go beyond western countries and include Sunni majority states, in order to reject the kind of nihilism that Isis projects.

Speaking at his closing press conference, David Cameron added that a military commitment was required, but that the government was not at the stage of making decisions on air strikes.

A fighter jet lands on the flightdeck of the US navy aircraft carrier USS George HW Bush after flying missions over Iraq. Photograph: Hasan Jamali/AP

The UK prime minister said what was needed was a combination of "intelligent politics, diplomatic pressure, long-term engagement, a comprehensive plan, as well as the potential for military or other aggressive action".

Cameron said: "Solving this problem has already taken military commitment. Britain has been dropping aid out of military planes. We have been flying spy planes over parts of Iraq. We have been providing the Peshmerga with arms. Clearly military commitment is required. What I have said is nothing is ruled out."

The US has launched more than 100 air strikes on Isis positions in northern Iraq in the past month to try to check the progress of the militants, who have seized a vast swath of Syria and Iraq.

On the question of whether it would be necessary to secure UN support for any deeper military action, the prime minister was evasive, saying: "The more the UN can say to back and support hopefully a new Iraqi government in its work and to condemn Islamist extremism the better."

Cameron added: "If we are going to deal with the problem of IS [Isis] we have to deal with it right across the board. It involves the same thing in Syria as we need in Iraq. Just as we need in Iraq a government that represents all of the people, Sunni, Shia, Kurd, so we need in Syria a transition to a government that represents all of the people."

He also said he would not put a specific time frame on how long it would take to squeeze Isis, saying only that it was a generational struggle. "It is wrong to think the cause of the problem is the particular fracture in a country like Iraq or Syria. The cause of the problem is the poisonous narrative of Islamists. Extremism bubbles up to the surface wherever there are fractures," he said.

Kerry said there would be many ways to take the fight to Isis. US officials cited the valuable expertise of America's allies such as British and Australian special operations, Jordanian intelligence, Turkish border control and Saudi Arabia's ability to cut off financing to radicals.

The first aim will be corral as many regional countries into the coalition ahead of a meeting of the UN security council hosted by the US president, Barack Obama, in the week of 22 September in New York.

The security council meeting, likely to be held during the UN general assembly and attended by Cameron, could lead to a resolution giving UN legality to any military action to drive out Isis. There will be intense diplomatic pressure placed on countries such as Russia, Qatar, Saudi Arabia and Iran to back the condemnation of Isis. Russia has already backed UN resolutions trying to cut off financial support to the militants.

Kerry stressed the length of the commitment necessary. "We have the ability to destroy IS. It may take a year, it may take two years, may take three years, but we are determined it has to happen. The effort to destroy and degrade IS will take time and persistence".

He added: "There is no containment policy for IS. They are an ambitious, avowed genocidal, territorial-grabbing, caliphate-desiring quasi state with an irregular army, and leaving them in some capacity intact anywhere would leave a cancer in place that will ultimately come back to haunt us."

He said Friday's initiative proved "we have the ability to come together, that our capacities of defence are not frozen in an old model that we cannot respond to something like this."

He added: "We very much hope that people will be as declarative as some of our friends around the table have been in order to be clear about what they're willing to commit, because we must be able to have a plan together by the time we come to (the United Nations general assembly). We need to have this coalesce."Philip Hammond, the British foreign secretary, who chaired the meeting with Kerry, said: "It's going to be a long campaign; not necessarily a military one, but a campaign to turn the tide, to cut off the funding, to undermine the recruiting, to cut off the support that they're receiving from some of the countries around the world and to push [them] back.

"We in Britain have made no commitment to take part in any air strikes as yet, but we'll certainly consider that possibility if we think that it is the best and most effective way to support a credible and inclusive Iraqi government."

British sources stressed military action was not imminent, saying Obama would not step up a gear until a new stable and plural government had been formed in Iraq. It is assumed that Britain and France with bases in the area would offer air support.

There was also concern at the optics of a meeting convened of leading western powers at a Nato summit when both Obama and Cameron have put huge emphasis on any Iraq intervention not being western-led.

Nato announced it would offer to build defence capacity in Iraq if requested by the new non-sectarian government due to be formed by the end of next week. The secretary general, Anders Fogh Rasmussen, said Nato would also co-ordinate the humanitarian airlift in Iraq as well as an information exchange on jihadi fighters returning to their home countries.

Chuck Hagel, the US defence secretary, is due to travel to Turkey next week to hold talks with President Recep Tayyip Erdogan. Turkey could be asked to be the military epicentre of any co-ordinated air strikes.

The short-term focus will remain Iraq, with sources indicating that no attack on Isis in Syria would be considered until more had been done to identify military targets, clarify legalities and build diplomatic support for a measure that risked strengthening Syria's president, Bashar al-Assad.

Cameron and Obama have both made clear they do not support forming an unholy alliance with Assad against Isis, saying Assad is part of the problem and not part of the solution.

A British official, speaking on condition of anonymity, said: "There is a growing sense that this is going to take more than we are doing... but it needs to be a measured, cautious approach."

In a sign of early support from the Middle East, the United Arab Emirates foreign ministry released an unusually strong statement condemning the atrocities committed by Isis.