Twitter says its security team, along with relevant law enforcement officials, is investigating the veracity of apparent death threats made against its employees by radical Islamists.

The threats reportedly showed up on a Twitter account with ties to the Islamic State rebel group that has beheaded reporters.

Twitter has 800 employees in San Francisco, but none were eager to talk to reporters on Tuesday. The social networking service has been taking down accounts the company believes are platforms for the terrorist group ISIS. It is believed that action is what prompted the threats posted on such an account, which has since been removed.

The original threatening posts were in Arabic and initially translated on the website Vocative. They reportedly said:

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

“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 world assassin waiting.”

Steve Weber, a terrorism expert at UC Berkeley, believes the tweets are intended to frighten, but are without substance. “Day-to-day employees there are probably in more danger walking across the street in San Francisco than the likelihood of being hit by a terrorist assassin inside the United States,” he said.

Marc Sandalow, associate director of the University of California’s Washington Center, said he believes ISIS is using the threats and the recent videotaped beheadings of journalists to raise its profile on the world stage, but since President Obama’s initial statements discounting ISIS, the group’s soldiers have taken control of a significant amount of territory in Iraq and Syria.

Weber says “that has moved the discourse in Washington from ‘Maybe this thing is just going to go away’ to ‘We need to make sure that this thing goes away.’”

The president laid out his strategy for going after ISIS to members of Congress on Tuesday. Wednesday night, he briefs the nation at 6 p.m. PT in an address that will air live on NBC.