An American citizen who allegedly traveled to Syria and became a sniper and weapons instructor for ISIS has been charged by federal authorities with supporting the terrorist organization, prosecutors said Friday.

Ruslan Maratovich Asainov, a naturalized U.S. citizen born in Kazakhstan, was charged with providing and attempting to provide material support to a foreign terrorist organization, according to a criminal complaint unsealed in Brooklyn federal court.

“The defendant, a naturalized U.S. citizen residing in Brooklyn, turned his back on the country that took him in and joined ISIS, serving its violent ends in Syria and attempting to recruit others to its cause,” stated United States Attorney Richard Donoghue for the Eastern District of New York. “Our counterterrorism prosecutors and law enforcement partners will continue working relentlessly to hold accountable those like the defendant who have supported ISIS’s violent agenda.”

According to the unsealed complaint, Asainov, 42, first traveled to Turkey in late 2013. From there, he entered into Syria and allegedly enlisted to join ISIS as a fighter, according to the charges.

Based on information from a confidential informant who said he communicated with Asainov regularly between August 2014 and March 2015, Asainov said that since joining ISIS his "faith in Islam had been renewed" and would send photos of himself holding a "large-caliber assault rifle, fitted with a scope."

Asainov at one point allegedly tried to recruit the informant, telling him ISIS would give him "a job, housing, food and a $50 stipend per month," according to the filing.

In a message to an associate, Asainov allegedly bragged that ISIS was "the worst terrorist organization in the world that ever existed" and expressed his hopes to die in battle.

Asainov was first detained overseas by the Syrian Democratic Forces (SDF) before being transferred to to the U.S. and into FBI custody.

He's expected to make his first appearance in court later Friday afternoon in Brooklyn.