President Barack Obama urged a broad front against the Islamic State as NATO leaders gathered in Wales Thursday with Britain and France weighing joining US air strikes in Iraq.
Pressure on Western governments to take firm action against the jihadists in Iraq and Syria has risen sharply after the brutal videotaped execution of a second American journalist and a threat to kill a captive British aid worker.
The beheading of 31-year-old reporter Steven Sotloff came amid mounting evidence from the United Nations and human rights groups of the scale of the atrocities committed by IS fighters in northern Iraq and eastern Syria against ethnic and religious minorities.
"We know that if we are joined by the international community, we can continue to shrink (IS's) sphere of influence, its effectiveness, its financing, its military capabilities," Obama said.
"And the question is going to be making sure we've got the right strategy, but also making sure that we've got the international will to do it," he said in Estonia before heading to the summit in Wales.
With one of its nationals also under threat of beheading, summit hosts Britain said it would not rule out taking part in air strikes if necessary.
"I can assure you that we will look at every possible option to protect this person," Foreign Secretary Philip Hammond said.
And French President Francois Hollande likewise raised the prospect of a military response to the threat posed by IS.
"The head of state underlined the importance of a political, humanitarian and if necessary military response in accordance with international law," his office said.
- 'Mediaeval savagery' -
Obama pledged that justice would be done to the killers of 31-year-old reporter Steven Sotloff, wherever they hid and however long it took.
Obama will lead a UN Security Council session on the threat of foreign fighters in Iraq and Syria on September 25, a US official said Wednesday.
His Secretary of State John Kerry revealed he was working to forge a global coalition to fight the "mediaeval savagery" of Islamic militants terrorising a swathe of Syria and Iraq.
IS posted video footage on the Internet of Sotloff's beheading, confirmed as authentic by Washington, which sparked outrage around the world.
Signup to our newsletter and follow us on Facebook and Twitter!
It said the journalist's killing, which came on the heels of its beheading last month of another US reporter, James Foley, was in retaliation for expanded US air strikes against its fighters in Iraq during the past week.
It warned that a British hostage would be next unless London backs off from its support for Washington's air campaign.
Britain has so far only carried out reconnaissance flights in support of the US air campaign from its base in Cyprus.
France has joined Britain and the United States in air-dropping relief supplies to stricken civilians in northern Iraq, while other NATO allies, including Germany, have joined in flying arms supplies to Kurdish forces battling IS.
Obama said Washington was determined to halt the IS threat but warned it would depend on close cooperation with partners in the region.
- Sotloff family tribute -
The United Arab Emirates voiced its readiness to "take needed measures", as Iraq condemned the latest beheading as "an act of savagery and evil" that showed the urgency of defeating the jihadists.
British Prime Minister David Cameron said the execution video depicted an "absolutely disgusting, despicable act" and chaired a meeting of security chiefs to discuss how to tackle the IS threat.
The masked executioner in the video spoke with a London accent and claimed to be the same man, confirmed by UK security services as a Briton, who beheaded Foley.
At the end of the five-minute recording, the militant threatens another captive, identified as British aid worker David Cawthorne Haines.
London has maintained a media silence about the kidnapping and there were few immediate details about when or how he was abducted.
Sotloff's family paid moving tribute to the 31-year-old journalist, remembering a gentle soul with a fondness for junk food and golf who was fiercely committed to reporting.
"He was no war junkie, he did not want to be a modern-day Lawrence of Arabia: he merely wanted to give voice to those who had none," Sotloff family spokesman Barak Barfi said.