US vice president vows to pursue IS to 'gates of hell'

The United States will pursue Islamic State (IS) militants all the way to the gates of hell, said US Vice President Joe Biden.

The group released a video Tuesday on the Internet that showed the beheading of American journalist Steven Sotloff, just two weeks after the group released another video of the beheading of another American journalist, James Foley.

Israeli media reported that Sotloff held joint US-Israeli nationality.

American intelligence verified the authenticity of the video Wednesday morning. 

"When people harm Americans, we don't retreat, we don't forget," Biden said Wednesday during a speech in New Hampshire.

"We will follow them to the gates of hell until they are brought to justice – because hell is where they will reside."

US Secretary of State John Kerry echoed the vice president’s remarks.

He noted that the effort to free the remaining American hostages in Syria continues, adding that "those who have murdered James Foley and Steven Sotloff in Syria should know that the United States will hold them accountable too, no matter how long it takes."

'A brutality of barbaric nature'

Meanwhile, US Secretary of Defense Chuck Hagel said Wednesday that a coalition has to be established to fight IS militants "with a sense of urgency."

"They control half of Iraq today. They control half of Syria today. We better be taking them serious," Hagel told CNN.

"They are better organized. They’re better funded. They have more capability. They’re better structured. There is a dangerous ideology of a brutality of barbaric nature that we’ve not seen before."

Hagel emphasized that the US would not have any combat role on the ground in Iraq but, in response to a question about extending operations to Syria, also said air strikes would not be enough to defeat the militants. 

The US has been carrying out air strikes against the group's positions in Iraq since early August but the group's ability to transport fighters and equipment across the border with Syria has raised questions about whether destroying their bases in Syria is necessary to defeat them. 

Hagel also said that up to 100 US nationals had joined the Islamic State militants.