The incident took place in the early hours of Monday morning after a backpack containing the object and four others was found near a train station in New Jersey.
It followed two explosions in the Chelsea district of Manhattan, New York, on Saturday night which injured 29 people, one seriously.
The federal authorities are reported to have detained five people in connection with the incident
Police are yet to link the two incidents officially although off-the-record briefings indicate they believe the same person is behind the explosion.
The latest incident comes following a stabbing attack at a Minnesota shopping centre over the weekend which saw nine people injured.