Vice President Joe Biden
Vice President Joe BidenAFP photo

U.S. Vice President Joe Biden on Wednesday issued a sharp warning to the Islamic State group, 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, according to CNN. "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 IS militants Tuesday, two weeks after James Foley was executed in the same horrific manner on video.

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

"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.

U.S. Defense Secretary Chuck Hagel also addressed the IS issue on Wednesday, telling CNN that Washington’s goal is to “degrade and destroy” the terrorist group.

"We are aware of over 100 U.S. citizens who have U.S. passports who are fighting in the Middle East with (IS) forces," Hagel said. "There may be more, we don't know."

"We know they're a threat," he added, without saying whether or not there is a specific threat to the U.S. homeland. "We know they're brutal. We know they are ... something that we have never seen before ... there's a dangerous, dangerous ideology of brutality of a barbaric nature that we have not seen before. So my job as secretary of Defense is not to second-guess what may be or what's going to be."

Meanwhile on Wednesday, President Barack Obama vowed that the United States would not be intimidated by the beheading of Sotloff, but acknowledged the fight against the IS would take time.

Obama pledged that justice would be done to the IS murderers who brutally beheaded Sotloff, who was also an Israeli citizen, wherever they hid and however long it took.

Obama said the whole world had been repulsed by the barbarism of Sotloff's murder, but "we will not be intimidated. 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."