The bomb detonated on Saturday in New York, and a device found nearby, were both shrapnel-filled pressure cookers – similar to the bombs used at the 2013 Boston marathon, US media report.
Citing officials, separate reports said both had mobile phones and Christmas lights as makeshift detonators.
The blast, in the Chelsea area of Manhattan, injured 29 people.
The FBI said it stopped a “vehicle of interest” in Brooklyn on Sunday 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.
The Manhattan blast followed a pipe bomb explosion on the route of a charity race in New Jersey.
Investigatorsare also examining a suspicious device found near a train station in Elizabeth, New Jersey, late on Sunday.
Elizabeth Mayor Christian Bollwage said a bomb squad had determined the device containing wires and pipes could be a live bomb.
Reporters for two US news outlets said a loud explosion was heard in the area early on Monday.
New York Governor Andrew Cuomo said a second device discovered over the weekend in New York City appeared to be “similar in design” to the exploded device.
It was found four blocks from the site of the blast and was removed and later destroyed in a controlled explosion. No-one was hurt.
Some 1,000 extra security personnel are being deployed to New York’s transport hubs.
Authorities had described the weekend bombings in New York and New Jersey, along with a stabbing attack in Minnesota, as acts of terror 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.
Daesh [Arabic acronym for “ISIS” / “ISIL’] said the suspected attacker in Minnesota was one of the group’s “soldiers”, although it is not clear whether it was involved in planning the assault.
The Chelsea explosion occurred at about 21:00 [01:00 GMT on Sunday] on West 23rd St. The force of the blast blew out windows and could be heard several blocks away.
Some reports said the bomb went off in a black metal construction toolbox, others that it was in a rubbish bin.
Chelsea is among the most fashionable districts of Manhattan and its restaurants are usually crowded at the weekend.
Mayor Bill de Blasio said there would be a “bigger than ever” police presence in New York in the coming week.
On Tuesday, President Barack Obama and other world leaders are due to attend the UN General Assembly in New York.
Source: News Agencies, Edited by website team
19-09-2016 | 12:07