Police cordoned off a section of New York’s Times Square today to investigate what was described as a small explosion at a military recruiting office.
The explosion caused some damage but no injuries, police said.
NYPD Commissioner Ray Kelly said the device, a low explosive in an ammunition box, was “not particularly sophisticated”.
“But this type of explosive could certainly cause injury, or even death,” he said.
Mr Kelly said one witness saw an individual riding on a bicycle on the same traffic island as the recruiting station “in a suspicious manner”.
“This individual was wearing a hood and dark-coloured clothing. He was also wearing a backpack,” Mr Kelly said.
He added that the witness did not see this person’s face, however.
Mr Kelly also said the US authorities were studying video footage from the Times Square area, which is well covered by surveillance systems.
Cars and police tape began blocking vehicles from entering the area at around 5am local time.
Members of the police department’s bomb squad and the fire department were in the area surrounding the office which had a damaged front window.
Guests at the nearby Marriott Marquis hotel said they heard a “big bang” and could feel the building shake. They said a large plume of smoke was also visible after the explosion.
Local TV stations said subway trains were being prevented from entering the Times Square station during the investigation.
New York mayor Michael Bloomberg said: “The fact that this appears to be deliberately directed at the recruiting station insults every one of our brave men and women in uniform stationed around the world fighting to defend our freedom and the things that we hold so dear.”
Speaking at a joint press conference with Commissioner Kelly and city officials in Times Square, just yards from the site of the blast, Mr Bloomberg said: “Second, and I especially want to direct this to the people watching around this country and around the world, New York City is back and is open for business.
“People are going about their business, shopping, working and sightseeing. They are not intimidated.
“Whoever the coward was that committed this disgraceful act on our city will be found and prosecuted to the full extent of the law.
“We will not tolerate such attacks, nor will we let them destroy our freedom to live peacefully and safely in the greatest city of the world.
“In a moment, I’ll continue to do exactly that with my day, and I think all New Yorkers should do the same.”