President Obama made his strongest statements yet against the Islamic State of Iraq and Syria (ISIS) on Wednesday, promising that the U.S. will “degrade and destroy” the extremist group after they beheaded a second American journalist.

“Our objective is clear and that is to degrade and destroy ISIL so it’s no longer a threat—not just to Iraq but also to the region and to the United States,” Obama said, referring to ISIS by their alternate name. Close video Obama: US objective to degrade, destroy ISIL President Obama discusses the second death of an American journalist at the hands of extremist group ISIS and how the U.S. must respond. President Obama discusses the second death of an American journalist at the hands of extremist group ISIS and how the U.S. must respond. share tweet email Embed

On Tuesday, ISIS released a video of the beheading of Steven Sotloff, 31, a freelance journalist who worked for Time and Foreign Policy and was seized in Syria last August. His killer appears to be the same masked jihadist who killed James Foley exactly two weeks prior. The video’s authenticity was confirmed by President Obama and American officials early Wednesday.

Related: Letter from journalist James Foley details detention

The death of the Florida-based journalist has redoubled calls for expanded military action in the region, particularly airstrikes in Syria where the group is headquartered. Obama, speaking from Estonia just hours after agreeing to send 350 more troops into Iraq to protect the country’s diplomatic efforts, promised that “justice would be served.” Close video US sending 350 more troops to Baghdad embassy NBC News Chief Foreign Correspondent Richard Engel joins Rachel Maddow from the Turkish-Syrian border to discuss how terrorism has motivated US leaders to take military action. NBC News Chief Foreign Correspondent Richard Engel joins Rachel Maddow from the Turkish-Syrian border to discuss how terrorism has motivated US leaders to take military action. share tweet email Embed

The president said a combination of regional cooperation, airstrikes, and ground efforts would defeat ISIS.

“The first phase has been to make sure that we’ve got an Iraqi government that is in place and and we are blunting the momentum that ISIL was carrying out and the airstrikes have done that. Now what we need to do is make sure that we’ve got the regional strategy in place that can support an ongoing effort, not just in the air but on the ground to move forward,” he said. “It’s something that over time is gonna be effective.”

Related: Top Democrat Feinstein says Obama ‘too cautious’ on ISIS strategy

Obama said that expanding the military operation into Syria would likely require congressional approval – “It’s very important from my perspective that when we send our pilots in to do a job, that we know this is a mission that’s going to work … that we’ve made the case to Congress and to the American people” – but said he was confident the country could stop the extremist movement.

“Our objective is to make sure that ISIL is not an ongoing threat to the region and we can accomplish that,” he added.

In both videos showing the beheadings of the journalists, a masked ISIS militant says their executions are a response to American airstrikes in the region. That mission, which began with the limited goal of protecting religious minorities and U.S. assets threatened by ISIS, included humanitarian air drops to bring relief to thousands of Yezidis – members of an ancient religious sect – who were trapped on Mount Sinjar in northern Iraq without food or water. On Monday, the president informed Congress he’d broadened those strikes to aid a northern town where civilians were similarly trapped.

“Today our country grieves with [Sotloff’s family],” Obama said. “Whatever these murderers think they can achieve by killing innocent Americans like Steven, they have already failed.”

Sotloff’s mother made an emotional plea last week, begging his captors to release him. ““As a mother, I ask you to be merciful and not punish my son for matters he has no control over,” she said.

In his address, the president briefly eulogized the fallen American.

“Steven’s life stood in sharp contrast to those who murdered him so brutally – they make the absurd claim that they kill in the name of religion, but it was Steven, his friends say, who deeply loved the Islamic world. His killers try to claim that they defend the oppressed, but it was Steven who travelled across the Middle East risking his life to tell the story of Muslim men and women demanding justice and dignity.”