A bomb that exploded in New York City was an act of terrorism, Governor Andrew Cuomo says, but no link to international groups has been found.
Mr Cuomo said significant damage had been caused and “we were lucky there were no fatalities”.
Saturday night’s blast in Manhattan injured 29 people.
Some 1,000 extra security personnel are being deployed to NY transport hubs.
Mr Cuomo said: “Whoever placed these bombs – we will find them and they will be brought to justice.”
A second device – a pressure cooker attached to wiring and a mobile phone – had been found four blocks from the site of the explosion in the Chelsea district and was removed safely.
Addressing reporters on Sunday near the site of the explosion, Mr Cuomo said: “A bomb exploding in New York is obviously an act of terrorism.”
But he said that, as yet, no international organisation such as so-called Islamic State had claimed they were behind it.
Mr Cuomo said: “We will not allow these type of people and these type of threats to disrupt our life in New York. This is freedom. This is democracy, and we are not going to allow them to take that from us.
“They want to instil terror. They want to make you worry about going into New York. We’re not going to let them instil fear.”
He said the two devices in New York appeared similar in design, but different from the pipe bomb that detonated earlier on Saturday on the route of a charity race in New Jersey.
That explosion caused no injuries.