Five people from three different law enforcement agencies were injured during Thursday's training exercise when a device unexpectedly exploded in Pennsylvania, the FBI said.
The explosion occurred during explosives response training with local, state and federal agencies at SCI Phoenix prison. Members of the bomb squad were installing an explosive device into a vehicle for training purposes when it reportedly exploded prematurely.
The cause of the explosion has not been disclosed.
Five bomb technicians were wounded: three with the Montgomery County Sheriff's office, one Pennsylvania State Police officer and an FBI agent from Philadelphia, the FBI said.
They were all taken to hospitals. The injured FBI agent was treated and released Thursday. The injuries of the others vary; some were "significant" but none appeared to be non-life threatening, the FBI said.
"Our thoughts and prayers are with all the wounded and their families and colleagues," the FBI said Friday.
The FBI is investigating the incident.
Images from the scene show a burned-out car surrounded by blackened grass. The vehicle did not appear to be bent or mangled by an explosive blast, however.
Fox News' Anders Hagstrom contributed to this report.