NEW YORK - Investigators scrambled to find out who planted a bomb that rocked a bustling New York City neighbourhood and why Sunday, scouring shrapnel, forensic traces and surveillance video for any link to an unexploded pressure-cooker device found a few blocks away.
There seemed to be more questions than answers hours after the Saturday night blast that injured 29 people in Manhattan. All of them have since been released from the hospital.
"We just know there was a bombing," Mayor Bill de Blasio said at briefing at New York Police Department's headquarters. "That much we do know."
Democratic Gov. Andrew Cuomo, who toured the site of the blast in Manhattan's Chelsea neighbourhood, said there didn't appear to be any link to international terrorism. He said a second device found blocks away from the bombing appeared "similar in design" to the first.
That device — described by a law enforcement official as a pressure cooker with wires and a cellphone attached to it — was removed early Sunday morning by a bomb squad robot and is being examined by forensic experts.
The official spoke to The Associated Press on condition of anonymity because the official wasn't authorized to speak publicly about an ongoing investigation.
A pipe bomb explosion in Seaside Park, New Jersey, before a charity 5K race to benefit Marines and sailors earlier Saturday didn't appear to be connected to the Manhattan bombing, and each bomb contained different materials, officials said, but added that they weren't ruling anything out yet. The race was cancelled and no one was injured.
The New Jersey device contained evidence of a black powder, while the device that exploded in Manhattan had residue from an explosive called Tannerite, said a federal law enforcement official.
The official wasn't authorized to discuss details of the ongoing investigation and spoke to the AP on the condition of anonymity.
Tannerite is often used in target shooting to mark a shot with a cloud of smoke and small explosion.
The bombing rocked the city's Chelsea neighbourhood, a mostly residential part of Manhattan's west side known for its art galleries and large gay population.
A federal law enforcement official told the AP on Sunday that the FBI was evaluating a claim of responsibility for the New York City bombing on the social blogging service Tumblr. The official, who wasn't authorized to discuss an ongoing investigation by name and spoke to the AP on condition of anonymity, said the FBI was aware of the posting and was working to determine its authenticity.
Witnesses described hearing a deafening blast, and surveillance video footage captured images of nearby windows being blown out by the explosion as people sprinted away from the scene.
"It was extremely loud, almost like thunder but louder," said Rudy Alcide, a bouncer at a nightclub near the blast.
Members of the FBI's Joint Terrorism Task Force are investigating the blast along with New York Police Department detectives, fire marshals and other federal investigators. As a precaution, Cuomo said he was deploying an additional 1,000 state troopers and members of the National Guard throughout New York City.
The first device, which exploded on West 23rd Street at about 8:30 p.m., appeared to have been caused by an improvised explosive device placed inside a toolbox in front of a building undergoing construction, the law enforcement official said.
The second device, found later inside a plastic bag on West 27th Street, appeared to be a pressure cooker with wiring and a cellphone attached to it, the official said.
Federal investigators in Quantico, Virginia, will examine evidence from the explosions in New York and New Jersey.
Associated Press writers Karen Matthews, Ezra Kaplan and Maria Sanminiatelli in New York and Eric Tucker, Kevin Freking and Alicia A. Caldwell in Washington contributed to this report.