In a developing story, a video released Tuesday by the Islamic State (IS) appears to show the beheading of kidnapped American journalist Steven Sotloff.

The White House has not confirmed the authenticity of the video, which was reported by the SITE monitoring service.

Sotloff was last seen in a video released by IS two weeks ago. After a masked man executed photojournalist James Foley, he approaches a kneeled Sotloff and issues a grave warning.

"The life of this American citizen, Obama, depends on your next decision," the IS member, cloaked in black, said to the camera.

Sotloff, 31, went missing in Syria in August 2013. In the video released today, he addresses President Obama directly.

"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?" he asked.

Foley's death was prompted by U.S. airstrikes in Iraq and Syria, and the missile attacks have continued in the weeks since. The IS member in the most recent video said that Sotloff's death is in retaliation for the continued military action.

"[As long as missiles] continue to strike our people, our knife will continue to strike the necks of your people," the terrorist said before appearing to kill Sotloff.

At the end of the video, IS threatens the life of British hostage David Cawthorne Haines.

On Aug. 27, Sotloff's mother issued a video pleading for IS to release her son.

"As a mother, I ask your justice to be merciful and not punish my son for matters he has no control over," she said, speaking directly to IS leader Abu Bakr al-Baghdadi.

"I ask you to use your authority to spare his life and to follow the example set by the Prophet Muhammad, who protected People of the Book. I want what every mother wants, to live to see her children's children, I plead with you to grant me this."

White House Press Secretary Josh Earnest said officials are investigating the video's authenticity, and stated that "our thoughts and prayers, first and foremost, are with Mr. Sotloff and Mr. Sotloff's family."