Obama: U.S. won't back down to ISIS

America's top defense official says the goal of the United States is to "degrade and destroy" the capabilities of ISIS fighters in Iraq and Syria, not contain them.

The statement by Defense Secretary Chuck Hagel came during an interview with CNN's Jim Sciutto on Wednesday, just hours after President Barack Obama said the United States will not be intimidated by the killers of two American journalists.

"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," the President said.

Obama's words followed the U.S. authentication Wednesday of an ISIS terror group video, released the day before, showing the beheading of journalist Steven Sotloff.

The killing is the second beheading of an American journalist in two weeks, and the militant group said it's a result of Obama's decision to conduct airstrikes in Iraq against ISIS, which also calls itself the "Islamic State."

"It makes you sick to your stomach, but it again reminds you of the brutality and barbarism that is afoot in some places in the world," Hagel said. "...It won't just recede into the gray recesses of history until we stop it."

All options -- with the exception of a ground invasion -- are on the table to address the threat posed by ISIS, Hagel said.

Those options include possible airstrikes in Syria, where ISIS has established a stronghold in and around the northeastern Syrian city of Raqqa.

Vice President Joe Biden added his own voice to the calls for justice, saying the United States will pursue the killers "to the gates of hell."

"As a nation, we are united, and when people harm Americans, we don't retreat, we don't forget," he said at an appearance near Portsmouth, New Hampshire.

"We take care of those who are grieving. And when that's finished, 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."