Sotloff beheading: Biden vows to chase IS to 'gates of hell'
US Vice President Joe Biden has said the US will follow the Islamic State militants who have killed two US journalists "to the gates of hell".
His comments come after President Barack Obama vowed the US would not be intimidated after IS militants released a video showing the beheading of journalist Steven Sotloff.
Mr Obama said the US would build a coalition to "degrade and destroy" IS.
Another US journalist, James Foley, was similarly killed last month.
Speaking on Wednesday, Mr Biden echoed Mr Obama's comments, saying the US would not stop until the militants are brought to justice.
Mr Biden said the American people "are so much stronger, so much more resolved" than any enemy can understand.
US Defence Secretary Chuck Hagel also reiterated the Mr Obama's comments, saying the US mission was to "degrade and destroy the capability of Isil to come after US interests all over the world, and our allies". Islamic State is also often referred to as Isil or Isis.
He also told CNN that air strikes in Syria was one of the options the Pentagon had presented to the president for his consideration.
Separately, the UK held a meeting of its emergency Cobra committee after threats to kill a British hostage who was also shown in the latest video.
Islamic State has seized large swathes of territory in Iraq and Syria in recent months, declaring a new caliphate, or Islamic state, under leader Abu Bakr al-Baghdadi.
The US has launched more than 120 air strikes in the past month to try to help Kurdish forces curb the IS advance.
After the latest video emerged, Mr Obama ordered the deployment of another 350 troops to Baghdad to protect US diplomatic facilities.
His announcement came as campaign group Human Rights Watch said it had uncovered new sites of Islamic State mass killings in the Iraqi city of Tikrit.
The militants are believed to have murdered more than 500 Iraqi soldiers after taking over a large Iraqi army base in June.
Speaking in Estonia, Mr Obama said the beheading was a "horrific act of violence and we cannot begin to imagine the agony everyone who loves Steven is feeling right now. Our country grieves with them".
"Those who make the mistake of harming Americans will learn that we will not forget, that our reach is long and that justice will be served," he said.
Analysis: BBC North America Editor Jon Sopel
If you are a president or prime minister, one of the most difficult waves to ride is the cry that "something must be done". From both Republicans and Democrats here in Washington the killing of Steven Sotloff has brought those calls to an understandable crescendo.
There is revulsion and shock over this second killing. But what to do is the question that the president and his advisors have been wrestling with.
What Mr Obama has said is that there will be no hiding place for those who perpetrated the murder, and the reach of the US is long.
To answer the "something must be done" question the famously cautious president has said he would build a coalition to "degrade and destroy" Islamic State. So now we're left with two other not insignificant questions - when and how.
And we have to conclude that despite the calls for action, it's not going to happen any time soon.
A spokesman for the Sotloff family had earlier indicated they believed the video was genuine, issuing a statement that said: "The family knows of this horrific tragedy and is grieving privately. There will be no public comment from the family during this difficult time."
US state department spokeswoman Jen Psaki said intelligence had determined that the Sotloff and Foley beheading videos were not shot at same time, with the Sotloff video shot after Foley.
Mr Sotloff, 31, who also held Israeli citizenship, was abducted in northern Syria in August 2013.
He had appeared in a video last month which showed James Foley being killed.
The latest video, entitled "A second message to America", is about two-and-a-half minutes long and was apparently recorded in a desert.
Next to a masked figure, Mr Sotloff reads out a text addressed to President Obama saying: "You've spent billions of US taxpayers' dollars and we have lost thousands of our troops in our previous fighting against the Islamic State, so where is the people's interest in reigniting this war?"
The militant spoke with a British accent similar to that of the man who appeared to carry out the beheading of James Foley.
The man says: "I'm back, Obama, and I'm back because of your arrogant foreign policy towards the Islamic State... despite our serious warnings."
He also threatens to kill the British hostage shown in the footage. The family of the British hostage have asked the media not to release his name.