 -- ISIS today claimed that the Ohio State University attacker was one of its "soldiers."

In a message circulated online from one of its media outlets, ISIS said an "insider source" reported that the OSU attacker Abdul Razak Ali Artan "is a soldier" of ISIS and "carried out the operation in response to calls to target citizens of international coalition countries," according to a translation by the SITE Intelligence Group.

ISIS has repeatedly called on its followers to conduct attacks in the U.S., but no evidence has emerged publicly to suggest ISIS had foreknowledge of the OSU plot. The language used in this claim is similar to that used when previous so-called "lone wolves" were believed to have acted independently of the terrorist organization.

A Facebook post suspected to have been written by Artan shortly before the attack does not include a pledge of allegiance to the terrorist organization, as in previous cases, but does say that if the U.S. wants the attacks to stop, it has to "make peace with 'dawla in al sham,'" which is how some ISIS followers have referred to the organization.

“I can’t take it anymore,” he purportedly wrote in the post, which has been reviewed by ABC News and appeared on a page that has since been disabled. “America! Stop interfering with other countries, especially the Muslim Ummah. We are not weak. We are not weak, remember that.”

Sources familiar with the investigation told ABC News the FBI increasingly suspects Artan was inspired by ISIS to carry out the attack. Investigators are still trying to determine if he was in contact with terrorists overseas.

The sources said that Artan purchased the knife Monday morning at a local Walmart shortly before the attack. The FBI has concluded interviews with Artan's family members but is seeking to interview others close to the assailant.

Several people were stabbed, though none fatally, after Artan drove a vehicle into a crowd and then emerged from the vehicle slashing at bystanders with a knife. Artan was shot and killed by a local policeman about a minute into the morning attack, officials said.

[EDITOR'S NOTE: A previous version of this report said the online post suspected to have been written by Artan did not make reference to ISIS. The post may in fact refer to ISIS under another name, "dawla in al sham."]