Steven Sotloff Beheading Video Is Authentic, President Obama Says

The barbaric acts have "stiffened our resolve," Obama says.

“Overnight, our government confirmed that, tragically, Steven was taken from us in a horrific act of violence,” Obama said.

Obama expressed sadness for Sotloff’s relatives, and said the barbaric acts “stiffen our resolve.”

“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,” he said.

Captured Journalist Steven Sotloff Noted for His Heartfelt War Reporting

Mother of American Hostage Pleads With ISIS 'Caliph' for Mercy

Video Appears to Show Beheading of Journalist James Foley

Sotloff is the second American killed by someone professing to be a member of the group. In the video, which appeared online Tuesday, Sotloff addresses the camera, saying, “I’m sure you know exactly who I am by now and why I am appearing.”

“Obama, your foreign policy of intervention in Iraq was supposed to be for preservation of American lives and interests, so why is it that I am paying the price of your interference with my life?” the journalist says calmly as the black-clad militant holds a knife casually at his side.

The 31-year-old reporter studied journalism at the University of Central Florida, according to the Orlando Sentinel. His articles online show heartfelt reporting about the brutality of the Syrian war.