A Twitter account associated with ISIS, also known as the Islamic State, issued disturbing threats Monday, calling for the assassination of Twitter employees in San Francisco, according to a number of news outlets.

The ominous tweets came as the social media company has sought to crack down on accounts associated with ISIS and propaganda posts from the terror group, including grisly videos of executions.

The account, @dawlamoon, has since been suspended, but it is purportedly linked to Al Nusra Al Maqdisia (The Supporters of Jerusalem), according to Vocativ, one of the first outlets to pick up the story. The group reportedly pledged its allegiance to ISIS in February, though it wasn’t clear what, if any, formal ties the group had to ISIS.

The tweets were all written in Arabic, but Mashable had translated versions.

“The time has arrived to respond to Twitter’s management by directly attacking their employees and physically assassinating them,” one tweet read.

“Every Twitter employee in San Francisco in the United States should bear in mind and watch over himself because on his doorstep there might be a lone wolf assassin waiting,” read another.

All of the tweets were accompanied by a hashtag that translated to “the concept of lone wolf attacks.”

Twitter would’t say whether it was heightening security at its downtown San Francisco headquarters, saying only that its “security team is investigating the veracity of these threats with relevant law enforcement officials.”