Twitter says it is blocking accounts related to "graphic imagery" after the Islamic State released a video that shows the beheading of American photojournalist James Foley, who was kidnapped in Syria nearly two years ago.
U.S. intelligence has determined that the video is real.
Twitter CEO Dick Costolo tweeted Wednesday morning, "We have been and are actively suspending accounts as we discover them related to this graphic imagery. Thank you."
Costolo linked to a New York Times article about the video.
Twitter spokesman Nu Wexler confirmed the tweet with the Associated Press and referred further questions to a company policy page.
"Twitter allows immediate family members of someone who dies to request image removals, although the company weighs public interest against privacy concerns," reports the AP.
A reporter for Radio Sawa, a U.S.-funded Arabic-language radio station, first reported news of the video, including images and a link to the video. Twitter briefly suspended the reporter's account.
Twitter also suspended an account belonging to the Islamists' media arm. The Islamic State has turned instead to opening accounts on another social media platform called Diaspora, the BBC reports.
Costolo's tweet followed online calls to not share the video or images of the purported beheading, using hashtag #ISISmediablackout. ISIS refers to the Islamic State of Iraq and the Levant, one of the former names of the extremist Islamist militants.
Twitter user @LibyaLIberty appeared to start the hashtag, posting on Tuesday, "From here on out, I won't share any photo or video of violence intentionally recorded & released by ISIS for propaganda. #ISISmediaBlackout"
"Stop sharing this video. Stop giving them attention. Have respect for the human life lost," another user tweeted.
But others on Twitter pointed to the need to shine a light on atrocities.
"I don't agree with #ISISMediaBlackout," wrote Twitter user @LCplSwofford. "Sometimes people need be confronted with reality. People are more likely to care when there's images."
User @hypersemIs asked, "#ISISmediaBlackout a prudent strategy? Don't journalists have a responsibility to report murder/incitement to murder?"
USA TODAY Network has requested comments from Twitter.
Foley is one of an estimated 30 journalists who have gone missing during Syria's three-year civil war.