The FBI said Monday night that it was searching a Pennsylvania storage unit as part of its probe into an “ISIS-inspired terrorism” incident outside the New York City mayor's mansion over the weekend.

Chaos broke out near Gracie Mansion on Sunday after explosive devices were thrown during protests that were clashing with each other. Officials confirmed that one device was a real homemade explosive that could cause serious damage.

The FBI said in a social media post that its New York Joint Terrorism Task Force was conducting the search in Pennsylvania. It was not immediately clear what investigators were searching for or who the unit belonged to.

"The FBI is conducting a court authorized search of a storage unit in Pennsylvania related to the investigation into the incident near Gracie Mansion," the bureau said on X. "The FBI New York Joint Terrorism Task Force, along with our partners at the NYPD, will continue pursuing all leads and tips."

The bureau said Tuesday that the search of the storage unit revealed explosive residue and that special technicians with the FBI conducted a controlled detonation to "ensure the safety of law enforcement and others in the area."

According to investigators, an 18-year-old counter-protester reportedly lit and threw a smoking device toward the protest area and then tried to light another one that was given to him by another person. 

Both suspects, who have been identified as Ibrahim Kayumi, 19, and Emir Balat, 18, were charged in connection with Saturday's incident. 

The charges include unlawfully possessing and using a “weapon of mass destruction,” transporting explosives and attempting to aid a “designated foreign terrorist organization,” according to NBC News.