Five people have been taken into custody in connection with a bomb blast in the Chelsea area of Manhattan in New York City which injured 29, US media reports say.
The suspects were stopped by the FBI and police on a bridge between Brooklyn and Staten Island, ABC News reported.
The bomb was reportedly a homemade pressure cooker device packed with shrapnel, similar to those detonated at the 2013 Boston marathon attack.
A second device was found four blocks away and safely destroyed.
Authorities say the blast was an act of terrorism but have yet to give any details about the motive or suspects behind the attack.
New York governor Andrew Cuomo said the two devices in Manhattan appeared to be "similar in design". Photographs of the unexploded device showed a pressure cooker with a mobile phone and Christmas lights attached.
The blast came hours after a pipe bomb exploded in a rubbish bin on the route of a charity race in New Jersey. That explosion caused no injuries.
Police say the pipe bomb was different in design to the devices found in New York but they are exploring the possibility the two incidents are linked.
No group has said it carried out the attack and police have yet to give any information about the five suspects arrested on Sunday.
Earlier on Sunday, New York Mayor Mayor Bill de Blasio said: "Was it a political motivation? A personal motivation? We do not know."
"We know there was a bombing. We know it's a very serious incident. But we have a lot more work to do to be able to say what kind of motivation was behind this.
"All possible theories of what's happened here and how it connects will be looked at but we have no specific evidence at this point in time."
Mr Cuomo said: "Whoever placed these bombs - we will find them and they will be brought to justice."
Some 1,000 extra security personnel are being deployed to New York's transport hubs, police said.
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 bars and restaurants are usually crowded at the weekend.
Mr de Blasio said there would be a "bigger than ever" police presence in New York in the coming week.
On Tuesday, President Obama and other world leaders are due to attend the UN General Assembly in New York.
Governor Andrew Cuomo called it a politician's "nightmare scenario" - a late-night phone call with news of a crisis. The weekend's attacks in New York, New Jersey and Minnesota have put national security squarely back in the centre of the US presidential election.
A similar scenario unfolded in June following the Orlando nightclub shootings. That was an opportunity for Donald Trump - the "change" candidate who touts his hard line on security issues - to make his case... and he blew it. Mrs Clinton's lead grew as Americans soured on Mr Trump's bellicose response.
This time Mr Trump has been more measured, offering only condolences on Twitter. He did call the New York incident a "bombing" before official confirmation and said the US needed to "get tough", but that was hardly comparable to his jarring comments on Orlando.
Meanwhile, Mrs Clinton cautioned against premature conclusions - perhaps hoping her opponent would again overreact.
With the race tight once again and the first TV debate just over a week away, both candidates are under intense pressure to display their leadership qualities. Saturday's "nightmare scenario" was another test - and it probably won't be the last, according to BBC.