Vice President Joe Biden struck a significantly stronger tone against Islamic State than his boss on Wednesday, angrily declaring that 'we will follow them to the gates of hell!'

The United States plans to fight Islamic State until it is no longer a force in the Middle East and will seek justice for the killing of American journalist Steven Sotloff, President Barack Obama said on Wednesday.

He added destroying the militant group will take time because of the power vacuum in Syria, the abundance of battle hardened fighters that grew out of al-Qaeda in the Iraqi war, and the need to build coalitions, including with local Sunni communities.

Islamic State released a video on Tuesday showing the beheading of the U.S. journalist, the second American hostage to be killed within weeks, in retaliation for U.S. air strikes in Iraq.

“The bottom line is this, our objective is clear and that is to degrade and destroy (Islamic State) so that it’s no longer a threat not just to Iraq but also the region and to the United States," Obama told a news conference.

“Whatever these murderers think they will achieve with killing innocent Americans like Steven, they have already failed," Obama said. "They failed because, like people around the world, Americans are repulsed by their barbarism. We will not be intimidated."

"Those that 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," he said.

At home, top Obama administration officials punctuated Obama's warnings to the Islamic State.

"They should know we will follow them to the gates of hell until they are brought to justice. Because hell is where they will reside, hell is where they will reside," Vice President Joe Biden said during an appearance in New Hampshire.

In Washington, Secretary of State John Kerry called Sotloff's execution a "punch to the gut" and said the United States has used every military, diplomatic and intelligence tool it has to free hostages in Syria. 

Kerry said Sotloff was "brutally taken from us in an act of medieval savagery by a coward hiding behind a mask."

"We have taken the fight to this kind of savagery and evil before and, believe me, we will take it again," he said. "When terrorists anywhere around the world have murdered our citizens, the United States held them accountable no matter how long it took."

Obama is sending Kerry, Defense Secretary Chuck Hagel and counterterrorism adviser Lisa Monaco to the Middle East to work with regional partners on ways to battle Islamic State.

"This is not going to be a one-week or one-month or six-month proposition because of what's happened in the vacuum of Syria," Obama said. "It's going to take time for us to be able to roll them back."

British hostage

A masked figure in the video also issued a threat against a British hostage, a man the group named as David Haines, and warned governments to back off "this evil alliance of America against the Islamic State."

The purported executioner appeared to be the same British-accented man who appeared in an Aug. 19 video showing the killing of American journalist James Foley, and it showed a similar desert setting. In both videos, the captives wore orange jumpsuits.

"I'm back, Obama, and I'm back because of your arrogant foreign policy towards the Islamic State, because of your insistence on continuing your bombings and in Amerli, Zumar and the Mosul Dam, despite our serious warnings," the masked man said in the video.

"So just as your missiles continue to strike our people, our knife will continue to strike the necks of your people."

In the video, Sotloff describes himself as "paying the price" with his life for the U.S. intervention in Iraq.

Journalist, hostage

Sotloff, a 31-year-old freelance journalist from Florida, was kidnapped in Syria in August 2013.

A spokesman for the Foreign Ministry in Jerusalem revealed Wednesday that Sotloff was also an Israeli citizen, after withholding the information in a bid to stem the risks to the captive.

Sotloff's colleagues described him as a dedicated journalist and gifted writer who had filed in-depth reports from across the Middle East. He covered unrest in Libya for Time magazine in 2012 before his kidnapping in Syria.

Time Editor Nancy Gibbs said that Sotloff "gave his life so readers would have access to information from some of the most dangerous places in the world."

Sotloff's mother, Shirley, had appealed last Wednesday in a videotaped message to Islamic State's self-proclaimed caliph, Abu Bakr al-Baghdadi, appealing for her son's release.

Air strikes

The United States resumed air strikes in Iraq in August for the first time since the pullout of U.S. troops from the country in 2011.