WASHINGTON — The extremist group has put an unverified warning message on the Internet and suggested that more bloodshed will come following the attack in Garland, Texas last weekend.

ISIS had previously taken the credit for the shooting attack in Texas but the White House and other security experts are doubtful of the group’s claim. U.S. officials said the militant group has yet to provide evidence of it’s alleged direct involvement after two suspected extremists were shot and killed by police.

ISIS has boasted in a file-sharing site favored by ISIS supporters that it has “signed up” 23 new fighters for the U.S. attacks similar to Texas. The message was signed by Abu Ibrahim Al Ameriki. Authorities believe he is the same man who appeared in ISIS’ previous propaganda videos.

“Out of the 71 trained soldiers 23 have signed up for missions like Sunday, we are increasing in number. Of the 15 states, 5 we will name… Virginia, Maryland, Illinois, California and Michigan,” read the posted message. The warning went to say that the “brothers” police killed had given their bodies in plain view because ISIS was watching.

FBI director James Corney said in February that the agency is investigating in every state for possible signs of terrorist “sleeper cells.” He believes each state in the U.S. has homegrown violent extremists. 

An intelligence official said that U.S. officials were investigating the threat but finds it difficult to believe it came from the leaders of ISIS. The online threat may have come from a low-ranking fighter taking advantage of the incident in Texas.