The bomb detonated on Saturday in New York, and another device found nearby, were both shrapnel-filled pressure cookers - similar to the bombs used at the 2013 Boston marathon, reports say.
Citing top law enforcement officials, the New York Times said the two devices used flip phones and Christmas lights to detonate the explosive inside.
The blast, in the Chelsea area of Manhattan, injured 29 people.
The FBI denied news reports that five people had been taken into custody.
The second device was found four blocks from the site of the explosion and was removed safely.
New York governor Andrew Cuomo said it appeared to be "similar in design" to the exploded device.
Both were different from a pipe bomb that detonated earlier on Saturday on the route of a charity race in New Jersey, Mr Cuomo added. That explosion caused no injuries.
The unexploded second device was destroyed by police in a controlled explosion late on Sunday.
