Federal agents on Monday served search warrants in New Jersey and Pennsylvania as investigators probe a possible act of terrorism tied to explosive devices thrown during a protest in New York City.

A New York Police Department source told Fox News that devices hurled into the crowd were packed with nuts, bolts and screws, and contained a chemical substance inside a taped canister fitted with a fuse.

Emir Balat and Ibrahim Kayumi remained in custody as federal teams searched their homes in Bucks County, Pennsylvania, according to federal sources.

Investigators also executed a warrant at a related address in New Jersey.

This is a breaking news story; check back for updates.