A backpack containing multiple bombs was found Sunday night near an Elizabeth, New Jersey, train station, according to the FBI and the city’s mayor.
The suspicious device exploded as a bomb squad was attempting to disarm it with a robot, officials say.
The backpack had up to five devices, Elizabeth Mayor Chris Bollwage said. It was found around 9:30 p.m. in a wastebasket outside a neighborhood pub, about 500 feet from a train trestle. The two men who found the backpack thought it might contain something valuable, but they alerted police when they saw wires and a pipe on the devices, the mayor said.
No cell phones or electronic timing devices were found, Chris Bollwage said. No-one was hurt.
The discovery came after three attacks at the weekend – bombs in New York and New Jersey, and stabbings in Minnesota.
The explosion in New York’s Chelsea area injured 29 people.
In New York City, the FBI said it had stopped a “vehicle of interest” in Brooklyn on September 18 but made no arrests.
Five people were taken into custody for questioning, officials told US media. But a spokeswoman said no-one had been charged and the investigation was continuing.
A man seen on surveillance video has been described as a “person of interest” in the police inquiries.
Both the bomb that detonated on September 17 in Chelsea, and a device found nearby, were shrapnel-filled pressure cookers – similar to the bombs used in the attack on the 2013 Boston marathon.
They also used flip phones and Christmas lights designed to trigger the explosive, the New York Times said.
The two instruments appeared to be “similar in design”, New York Governor Andrew Cuomo said.
Some 1,000 extra security personnel are being deployed to New York’s transport hubs.
Authorities have described the weekend bombings in New York and New Jersey, along with a stabbing attack in Minnesota, as acts of terrorism and are trying to establish whether there are any links between them.
But they say they were so crude that it is unlikely an international group was behind them.
ISIS has said the suspected attacker in Minnesota was one of its “soldiers”. It is not clear whether ISIS was involved in planning the assault.