Nato leaders are convening in Wales today, and before the summit even officially begins the diplomacy has started in earnest.
David Cameron has said he will not rule out military action against Islamic State militants, who have killed two American journalists in recent weeks and are threatening to kill a Scottish aid worker.
In a BBC interview, Cameron said that if Britain was to join the US in launching airstrikes against IS its actions would have to be "properly thought through and patiently delivered", without going "over the heads of neighbouring states".
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He also ruled out paying a ransom to secure the hostage's release.
As well as the threat posed by IS militants abroad and at home, the Nato summit will also discuss the ongoing crisis in Ukraine.
In a mark of the seriousness with which the alliance views its deteriorating relationship with Russia, Ukrainian President Petro Poroshenko has been invited to brief world leaders on discussions he has had with Vladimir Putin.
According to The Times, "Russia will dominate the summit in Newport today", as leaders discuss how to address Moscow's suspected intervention in eastern Ukraine.
Nato summit: what will it achieve?
World leaders will gather in Wales this week for the first Nato summit since Chicago in 2012, and the first in the UK since Margaret Thatcher was the host in London in 1990.
Top of the agenda will be the growing instability in Ukraine and the future of Nato's engagement in Afghanistan. The summit will provide both challenges and opportunities for Wales.
Where will it be held and who is going?
It's taking place at Newport's Celtic Manor Resort, which hosted the 2010 Ryder Cup golf tournament, on 4 and 5 September. Some 150 heads of state and ministers will attend, including Barack Obama, Angela Merkel and Francois Hollande. The leaders' combined entourage will comprise around 10,000 support staff.
What will be discussed?
Top of the agenda will be the continuing tensions in Ukraine. That crisis could make this summit the most important Nato gathering since Prague in 2002, when Nato added seven members.
According to the Washington Post, by invading Ukraine just one week before the summit, Vladimir Putin effectively taunted Nato, which he believes lacks the will to challenge him on the matter.
However, Nato secretary general Anders Fogh Rasmussen told The Guardian the summit will overcome divisions within the alliance and agree to new deployments on Russia's borders. He hopes members will agree a "readiness action plan" over Ukraine.
What else?
Also on the agenda will be growing threats to Nato countries from Islamic State, rogue and fragile states, piracy, terrorism and cyber attacks. Nato says other topics to be discussed include "collective defence", military spending, deepening partnerships and the future of Nato's engagement in Afghanistan.
What does the summit mean for Wales?
A security headache, primarily. The summit will be the largest gathering of international leaders ever to take place in Britain. With various protests planned and terror threats expected, some 9,500 police officers drawn from 43 UK police forces will work in and around the site. Additionally, 12 miles of security fencing has been installed at keys sites in Cardiff and in Newport.
First Minister Carwyn Jones says the summit will be a "momentous occasion in the history of Wales" and a chance to boost business and tourism. David Cameron added: "We had the G8 in Northern Ireland, we had the Olympics in London, we've got the Commonwealth Games in Scotland - it is Wales' turn for one of these big events."
Nato summit: Obama and Cameron to demand more defence spending
1 September
At a Nato summit in Wales this week, Barack Obama and David Cameron will call on all members of the alliance to increase their defence budgets in line with commitments to maintain an expenditure of at least two per cent of their total GDP on their armed forces.
British military chiefs backed the call, accusing some states of "freeloading" on members who are fulfilling their obligations, including the US and the UK, the Daily Telegraph says. But some diplomats are expected to reject the criticism, arguing that the spending targets are "arbitrary".
Former senior military commanders also called on all members to meet their obligations. Sir Alan West, a former head of the Navy, said: "People in a number of countries have been willing to get a free ride and are not spending. If you look at Europe, it's only France and the UK who meet the target. Nato has to realise that it's no good having a broken force".
Sir Richard Dannatt, a former Army chief, said many European states needed to improve their current military capabilities. He said: "The sad fact is that with the exception of a small number of European Nato member states — which include the UK and France principally — the vast majority of the armed forces of other European states lack real usable capability and their governments often lack the political will to fund their armed forces properly."
Nato members attending the two-day summit in Newport are expected to debate how to respond to recent developments in Ukraine and Iraq.
But Xenia Wickett, the head of the USA program at Chatham House, told journalists that the Wales summit needs to be a "way station" rather than an "endpoint" in dealing with the complex global security situations the alliance is facing, USA Today reports.
"There's a risk that the summit becomes all about putting out fires rather than a more strategic one," she said. "The summit needs to pay attention to current events, but it also needs to look much further ahead in terms of where Nato as an organisation is going."
