New York police continued to search for clues on Sunday that might lead them to the bomber behind a blast that injured 29 in the city’s bustling Chelsea neighbourhood on Saturday night.
Investigators examined the scene of the explosion in Manhattan in or near a skip as well as a second unexploded bomb found four blocks away that appeared to be a home-made pressure-cooker device wired to what looked like a mobile phone.
All 29 people who were wounded in the explosion, mostly by flying shrapnel and debris from the explosion, have been treated and released from hospital, officials said.
New York governor Andrew Cuomo said the attack was clearly "an act of terrorism," while the city's mayor Bill de Blasio called it "an intentional act" but the motivation remains unclear. "Was it a political motivation? A personal motivation? We do not know," he said.
The blast occurred at around 8.30pm (around 1.30am Irish time) on West 23rd Street between Sixth and Seventh Avenues, a popular nightlife area on the west side of Manhattan. It is known for its large gay community and at weekends it has packed bars and restaurants.
Shattered windows
The second device, found in a plastic bag and similar to the bomb in the 2013 Boston Marathon blasts, was discovered on West 27th Street.
The blast sent bystanders running from the scene and shattered windows in nearby businesses, putting a city on high alert just a week after marking the 15th anniversary of the September 11th, 2001, attacks that killed almost 3,000 people in Manhattan.
“A bomb exploding in New York is obviously an act of terrorism,” said Mr Cuomo. “That’s how we’ll consider it. And that’s how we will prosecute it.”
An additional 1,000 New York State police officers and National Guard troops have been deployed to patrol bus and subway stations and airports.
Mr Cuomo said it was fortunate there were no fatalities given the force of the explosion. He promised to find the person or people responsible.
“Whoever placed these bombs, we will find them and they will be brought to justice,” he said. “We will not allow these kinds of people and these kinds of threats disrupt our life in New York.”
Federal investigators in Quantico, Virginia, were continuing to see if there was any connection between the blast and a pipe bomb explosion hours earlier in Seaside Park in neighbouring New Jersey that took place before a charity road race to benefit military personnel.
“At this point we do not have any specific evidence of a connection but that will continue to be considered. So we’re not taking options off the table,” Mr de Blasio told reporters.
Governor Cuomo said the materials used in the New Jersey bomb appeared to be different.
Witnesses recalled hearing a deafening blast. "Everything was shaking, the windows were shaking," Rudy Alcide, a bouncer at a nightclub near the scene, told Associated Press. "It was extremely loud, almost like thunder but louder."
Stabbings
US law enforcement was further on edge over stabbings in a shopping centre in St Cloud, Minnesota on Saturday evening. Nine people were stabbed by a man who was shot dead by an off-duty police officer in what the FBI called "a potential act of terrorism".
Police and witnesses said that the man, dressed in a private security company uniform, entered the shopping centre at around 7pm local time, made a reference to Allah and asked at least one person if they were Muslim before he attacked.
