TALLINN, Estonia — President Barack Obama said today that the United States will not be intimidated by Islamic State militants after the beheading of a second American journalist and will build a coalition to “degrade and destroy” the group.

Obama still did not give a timeline for deciding on a strategy to go after the extremist group’s operations in Syria.

“It’s going to take time for us to be able to roll them back,” the president said at a news conference during a visit to Europe.

The president’s comments came after he said the United States had verified the authenticity of a video released Tuesday showing the beheading of freelance reporter Steven Sotloff, two weeks after journalist James Foley was similarly killed.

Obama vowed the U.S. would not forget the “terrible crime against these two fine young men.”

“We will not be intimidated. Their horrific acts only unite us as a country and stiffen our resolve to take the fight against these terrorists,” Obama said.

Obama also sought to clean up the damage from his statement last week that “we don’t have a strategy yet” for dealing with the Islamic State group in Syria. Republicans quickly seized on the remark to argue the president lacks a coherent approach to fighting the extremist group.

“It is very important from my perspective that when we send our pilots in to do a job, that we know that this is a mission that’s going to work, that we’re very clear on what our objectives are, what our targets are,” Obama said.

In the Sotloff video, a masked militant warns Obama that as long as U.S. airstrikes against the militant group continue, “our knife will continue to strike the necks of your people.”