ISIL released a video on Tuesday showing a masked militant beheading a second American journalist, according to the private terrorism monitoring group SITE.

ISIL released a video on Tuesday showing a masked militant beheading a second American journalist, according to the private terrorism monitoring group SITE.

The White House said that it had yet to authenticate the footage, which SITE said showed 31-year-old freelance writer Steven Sotloff on his knees beside an IS fighter with a knife.

"If the video is genuine, we are sickened by this brutal act," State Department spokeswoman Jen Psaki said of the footage released by the militants, in which 31-year-old freelance writer Steven Sotloff appears to have been killed.

ISIL militants also threatened to kill a British hostage.