Story highlights Of the U.S. journalists' killers, vice president says, "We will follow them to the gates of hell"

"Because hell is where they will reside," he added. "Hell is where they will reside"

Biden referenced 9/11 and the Boston bombings as examples of American resolve

Vice President Joe Biden on Wednesday issued a sharp warning to ISIS militants, saying after the United States is done grieving the death of two American journalists, their killers will have to answer for their actions.

"They should know we will follow them to the gates of hell until they are brought to justice," he forcefully told an audience at an event on the New Hampshire-Maine border. "Because hell is where they will reside. Hell is where they will reside."

Biden opened his remarks in memory of Steven Sotloff, the journalist who was beheaded by ISIS militants Tuesday, two weeks after James Foley was executed in the same horrific manner on video. Foley was from New Hampshire, while Sotloff lived there for boarding school.

Describing the perpetrators as "barbarians," Biden vowed that Americans would not be frightened or intimidated by the heinous acts.

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"We came back after 9/11. We dusted ourselves off and we made sure that Osama bin Laden would never, ever again threaten the American people," Biden said. "We came back Boston strong, blaming no one but resolve to be certain that this didn't happen again."

"As a nation, we're united, and when people harm Americans, we don't retreat," he later said. "We don't forget."

The vice president, who's mulling a 2016 presidential bid, made his remarks at the Portsmouth Naval Yard in a speech about the economy. He was accompanied on stage by U.S. Sen. Jeanne Shaheen, a New Hampshire Democrat who's running for re-election this year.

Previewing Biden's trip, the campaign for former Republican Sen. Scott Brown, who's challenging Shaheen for her seat in this year's midterms, released a Web video that shows footage of the vice president supporting President Barack Obama's foreign policy, an agenda the Brown campaign labels a "failure."

'Degrade and destroy'

After Sotloff's killing, Obama faced a chorus of bipartisan calls from Congress to act more aggressively and come up with a concrete strategy to combat ISIS, beyond the already ongoing targeted air strikes.

Speaking Wednesday, Obama addressed his much criticized statement last week that he has no strategy on ISIS. He said he was referring to a military strategy in Syria that "might" require congressional approval.

"Our objective is clear. That is to degrade and destroy (ISIS) so it's no longer a threat," he said. "We can accomplish that. It's going to take some time, it's going to take some effort."

The president said the world needs a regional strategy to defeat the group.

"We've been putting together a strategy that was designed to do a number of things... What we have to make sure is we have a regional strategy in place," he said.