ISIS had recently threatened to kill U.S. journalist James Foley to avenge airstrikes the United States has conducted in Iraq, a senior U.S. official told ABC News.

The White House had been aware of the threat prior to the release of a video Tuesday night that appears to show the beheading of Foley and warns that militants will carry out a similar act against U.S. journalist Steven Sotloff, who went missing in August, the official said.