The FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are both on scene investigating the incident.
Officials say three men are dead after a auto exploded in Allentown Saturday night. Grim said he would probably be able to release the names Monday once their identities are confirmed and their families are notified.
Federal and local authorities are investigating a vehicle explosion in Allentown, Pennsylvania, killed at least one person.
"Loads of us in law enforcement" are confident "this was A.an isolated incident and B. there's no continuing threat", Martin added.
Many residents in the city located about 60 miles northwest of Philadelphia reported hearing or feeling the large blast, the Morning Call reported.
The FBI had earlier said it was working with other agencies and "to assess the situation and determine the cause, with public safety the bureau's highest priority". Authorities are seeking tips from the public to help solve the crime.
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"We also ask that the residents that live inside that area to shelter in place until further notice".
"The fire was insane", Carlos Perodin told the paper. Neighbors said they heard a loud boom, and some felt their house shake.
"The fire was insane", resident Carlos Perodin, who lives not far from the scene, told local media.
"This is real life and I'm shaking and freaking out while I'm running", she said.
The Red Cross tweeted it had set up a temporary shelter in the area.
Officials asked anyone who witnessed the blast or had information about it to contact investigators.