UPDATE — 5:15 a.m. ET: President Barack Obama reacted to the execution of American journalist Steven Sotloff, calling it a “horrific act of violence.”

“Today, the prayers of the American people are with the family of a devoted and courageous journalist,” Obama said during a joint press conference with Estonia President Toomas Hendrik Ilves.

Obama added that “whatever these murderers think they will achieve” they have “already failed” because the U.S. “will not be intimidated.”

“Our reach is long and justice will be served,” the president promised.

The video showing the beheading of American journalist Steven Sotloff is authentic, the U.S. confirmed Wednesday.

After analyzing the graphic footage, the intelligence community “reached judgement” and concluded the video does show the execution of Sotloff at the hands of Islamic State militants.

On Wednesday, the terror group released video depicting the gruesome beheading, titled “A Second Message to America.”

Speaking to the camera, Sotloff described himself as “paying the price” for America’s intervention in Iraq.

EDS NOTE: GRAPHIC CONTENT - This image made from video posted on the Internet by Islamic State militants and provided by the SITE Intelligence Group, a U.S. terrorism watchdog, on Tuesday, Sept. 2, 2014, purports to show journalist Steven Sotloff before he was beheaded. Sotloff had last been seen in Syria in August 2013 until he appeared in a video released online by the Islamic State group on Aug. 19, 2014, that showed the beheading of fellow American journalist James Foley. The Arabic text at the bottom of the frame translates to "Now is the time for my message." (AP Photo) AP Photo

This image made from video posted on the Internet by Islamic State militants and provided by the SITE Intelligence Group, a U.S. terrorism watchdog, on Tuesday, Sept. 2, 2014, purports to show journalist Steven Sotloff before he was beheaded. (AP Photo)

Beside him, a British-accented militant directly addressed President Barack Obama.

“I’m back, Obama, and I’m back because of your arrogant foreign policy towards the Islamic State, because of your insistence on continuing your bombings and [unclear] on Mosul Dam, despite our serious warnings,” he says, waving a knife. ”You, Obama, have but to gain from your actions but another American citizen. So just as your missiles continue to strike our people, our knife will continue to strike the necks of your people.”

The Islamic State is again threatening another captive, identified as a Briton, David Cawthorne Haines.

TheBlaze’s Madeleine Morgenstern contributed to this report.

Follow Oliver Darcy (@oliverdarcy) on Twitter