A group that monitors extremist activity on Wednesday called for the parent company of WordPress.com to shut down websites the group says are used by the Islamic State and al-Qaeda affiliates to publicize “vile” and violent acts, including videos of beheadings and other atrocities.

The Counter Extremism Project, a nonpartisan research and advocacy group based in New York, said U.S.-based tech companies have been providing crucial infrastructure for the propaganda of anti-American militant groups, often unwittingly. The group says several militant Islamic groups use the popular WordPress.com platform to host content on their propaganda sites.

Some tech companies have complied with requests to remove content when flagged by the Counter Extremism Project, and WordPress.com has done so as well in some instances. But overall, WordPress.com, citing concerns about free speech, has declined to comply with most requests despite several letters of complaint from the advocacy project since May, the group said. Wednesday’s letter was addressed to Automattic Inc., the San Francisco-based parent company of WordPress.com.

“We’re not talking about stuff that’s in a gray zone,” said David Ibsen, executive director of the Counter Extremism Project. “All of these kinds of violent videos have some sort of incitement [to violence] or propaganda purpose.”

He said that the images and other content cited in the letter clearly violate the “terms of service” for WordPress.com.

A spokesman for Automattic said the company was investigating the letter from the Counter Extremism Project. Among the policies listed on the WordPress.com website, it says, “While our service is designed to enable users to freely express their ideas and opinions, however controversial, safety is important to us. As such, we don’t allow websites of known terrorist groups or genuine calls for violence against individuals or groups on WordPress.com.”

The letter demanding that content be removed included an image showing the head of a dark-skinned man held by somebody wielding a bloody knife. The group said it was a still shot from an extremist site and downloaded this week.

Other troubling images included in the letter include a firing squad shooting people lying facedown in the dirt. One image from a video showed a man who had apparently been killed by a gunshot to the head, along with the words “This is the enemy of Allah.”

An earlier letter from the group cited a website that included images of militants and the text declaring that Jews, “crusaders” and those who don’t believe in Islam “will be overcome and gathered in Hellfire.”

Another extremist Web page cited by the group in one of its letters to WordPress.com said, “Oh brother, you have no excuse in front of Allah for avoid fighting al-Jihad. . . . Don’t you know Allah’s words: ‘Kill the polytheists where you find them and capture them and besiege them and sit and wait for them at every place of ambush.’ ”

Many tech companies have struggled to balance their commitments to free speech with varying legal requirements around the globe and also their own terms of service. Content including hardcore pornography, spam and copyrighted music or videos routinely gets removed by tech companies when flagged by users, but extremist propaganda often falls outside of such clear-cut categories.

“In our experience dealing with tech companies,” Ibsen said, “when they don’t want to do something, they talk about free speech, and when they do want to do something, they talk about terms of service.”

The Counter Extremism Project also shared correspondence from a WordPress.com employee named “Sal P.," who wrote in one email, “WordPress.com is deeply committed to free speech and will not take content down just because we find it offensive or disagree with the point of view.” It added that it would review the case if an individual or group appears on the U.S. government's Specially Designated Nationals and Blocked Persons List.

Wednesday's letter said that several of the groups maintaining sites on WordPress.com were covered by the federal list. Many of the individuals are masked or otherwise obscure their face in the videos depicting violence.