Islamic State threatens 'war' on Twitter co-founder

The Islamic State has declared a new target in its war on the West — a co-founder of Twitter.

Twitter has routinely shut down Islamic State social media accounts, particularly those that threaten or link to beheadings and other atrocities. The militant group, also known as ISIL or ISIS, posted an online threat Sunday warning Twitter co-founder Jack Dorsey that "your virtual war on the Internet will cause a real war on you."

Twitter issued a one-sentence statement saying that its "security team is investigating the veracity of these threats with relevant law enforcement officials."

The threat was posted in Arabic under a headline "Foundation for the conquest of Jerusalem for the Islamic State," and "Twitter a target for the caliphate."

The Islamic State is fighting to create an extremist state -- or caliphate -- across a wide area of Iraq and Syria.

"Jack, how will you protect your helpless employees when their necks are on the line and they become an official target for soldiers of the succession and their supporters among you?" the online post states. "What will be your response to their families and sons, and their plight in this failed war?"

The post includes a matted photo of Dorsey with a target on his face.

"From the beginning of this failed war, we've said that this is not your war," the ISIL post says. "But you did not understand and kept closing our accounts on Twitter, but we always come back.

Twitter rules note that "you may not publish or post direct, specific threats of violence against others." Also banned: "any unlawful purposes or in furtherance of illegal activities."

Twitter and other social media sites have been cracking down on Islamic State accounts since June, when a major offensive resulted in large swaths land falling into the militant group's hands. But the group's social media savvy and resilience have kept their campaign alive on the Internet.

Dorsey, 38, a web developer and entrepreneur, founded Twitter in 2006 with Noah Glass, Biz Stone and Evan Williams. Twitter has more than 500 million users, more than half of which remain active on the site.

Contributing: Dominique Bonessi