The mother of an American journalist held captive by militant group Islamic State released a video Wednesday appealing directly to the group's leader for his release.

"I am sending this message to you, Abu Bakr al-Baghdadi al-Quraishi al-Hussaini, the caliph of the Islamic State. I am Shirley Sotloff. My son Steven is in your hands," Sotloff said in the video, obtained by The New York Times.

"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."

Sotloff, 31, went missing in Syria last year while covering the conflict there. The Islamic State group released a video last week in which Sotloff is seen following the filmed decapitation of fellow journalist James Foley.

Islamic State, which has declared a caliphate in territory it has captured in Syria and Iraq, threatened to kill Sotloff if its demands are not met.