Obama Vows to 'Degrade and Destroy' Islamic State After Steven Sotloff Killing

US President Barack Obama warned the Islamic State that "justice will be served" in response to the Sunni extremist group's murder of American journalist Steven Sotloff.

An online video released on Tuesday appeared to show Sotloff, 31, being beheaded by an Islamic State militant. US officials have now confirmed the footage is genuine.

"Our objective is clear, and that is to degrade and destroy ISIL [the Islamic State] so that it's no longer a threat not just to Iraq but also the region and to the United States," Obama said, speaking at a joint press conference with his Estonian counterpart Toomas Hendrik Ilves in Tallinn this morning.

Obama's Estonia visit en route to NATO summit is all about keeping Putin at bay. Read more here.

"Whatever these murderers think they'll achieve by killing innocent Americans like Steven, they have already failed. They have failed because, like people around the world, Americans are repulsed by their barbarism. We will not be intimidated. Their horrific acts only unite us as a country and stiffen our resolve to take the fight against these terrorists. And those who make the mistake of harming Americans will learn that we will not forget, and that our reach is long and that justice will be served."

Obama added that he wished to see a regional strategy involving air strikes and actions on the ground to tackle the Islamic State, but acknowledged that it would not be easy. "Our objective is to make sure that ISIL is not an ongoing threat to the region. And we can accomplish that. It's going to take some time and it's going to take some effort."

Sotloff is the second US citizen to be killed by the Islamic State in this manner. The group released a similar video showing the murder of James Foley, also a journalist, two weeks ago on August 19, supposedly in revenge for US air strikes on its fighters in Iraq. Sotloff was also shown in that footage, and it was claimed that his life depended on Obama's next move. In both videos, the apparent killer was a masked, black-clad militant with a British accent. UK Foreign Secretary Philip Hammond told the BBC today that it appeared to be the same person.

Sotloff, a freelance journalist who had worked for Time and Foreign Policy, was snatched by the group when working in Syria in August 2013. The Israeli government confirmed today that he had dual Israeli citizenship, adding that it had previously withheld the information in an effort to avoid additional risk.

Israeli Foreign Ministry spokesman Paul Hirschson tweeted the following:

Cleared for publication: Steven Satloff was — Paul Hirschson (@paulhirschson)September 3, 2014

Sotloff was born in the US and raised in Miami, but emigrated to Israel in 2008 to study at Herzilya Interdisciplinary Center near Tel Aviv, according to local media reports.

UK Prime Minister David Cameron has condemned the killings as "utterly abhorrent and barbaric," adding that: "We will not waver in our aim of defeating terrorism."

Sotloff's family have said that they will not be speaking about his death, issuing a statement saying: "The family knows of this horrific tragedy and is grieving privately. There will be no public comment from the family during this difficult time."

However, Sotloff's mother, Shirley, previously made a personal appeal to the Islamic State's leader, Abu Bakr al-Baghdadi. In a video released on August 28, she said: "I ask you to use your authority to spare his life and to follow the example set by the Prophet Muhammad, who protected people of the book. I want what every mother wants; to live to see her children's children. I plead for you to grant me this."

The Islamic State is known to have a number of other hostages, including another hostage who also appeared in yesterday's video — reportedly British security expert David Cawthorne Haines.

A 26-year-old US aid worker was also kidnapped in Aleppo in 2013. The woman's family has asked that she is not named but said that, in exchange for her release, the militants have demanded a $6.6 million ransom and that attempted killer Aafia Siddiqui is released from jail in the US. Siddiqui was convicted in 2010 of attempting to murder Americans serving in Afghanistan and their Afghan colleagues and is currently serving an 86-year sentence.

Also today, the US announced that it would be sending 350 more military personnel to Iraq. The troops — a mixed group of army and marines — will be assigned to protect the American embassy in the capital of Baghdad and will not serve in combat roles.

Watch the entire VICE News documentary The Islamic State here.

Follow John Beck on Twitter: @JM_Beck