TOPEKA, Kan. — A man accused of plotting a suicide bomb attack on a Kansas military base to help the Islamic State group is mentally ill and was acting strangely days before his arrest, according to a Muslim cleric who said he was counseling him at the FBI’s request.

John T. Booker Jr., 20, of Topeka, was charged Friday with planning a suicide attack at Fort Riley, about 70 miles west of Topeka. Prosecutors allege he told an FBI informant he wanted to kill Americans and engage in violent jihad on behalf of the terrorist group, and said he believed such an attack was justified because the Quran “says to kill your enemies wherever they are,” according to a criminal complaint.

The top federal prosecutor for Kansas also charged another Topeka man, Alexander E. Blair, 28, with failing to report Booker’s plans to authorities. The complaint alleges that Blair and Booker shared some “extremist views” and that Blair loaned Booker money to rent space to build and store a bomb.

Imam Omar Hazim of the Islamic Center of Topeka said two FBI agents brought Booker to him last year for counseling, hoping to turn the young man away from radical beliefs. Hazim said the agents told him that Booker suffered from bipolar disorder, characterized by unusual mood swings that can affect functioning.