New York police on Monday hunted a middle aged white male seen near a car bomb in Times Square that sparked a new terrorist alert and authorities discounted an Al-Qaeda link.
The man in his 40s was caught on a security camera taking his shirt off near the car just before the alert was raised and police cleared thousands of tourists away from the packed theatre district, officials said.
President Barack Obama vowed to track down the attackers and investigators said there were several strong leads as to who abandoned the Nissan Pathfinder utility vehicle with a large, spluttering homemade bomb inside late Saturday.
Police studied footage from 82 security cameras around Times Square and eviudence from the car and bomb, which were hauled to New York police laboratories.
One film sequence showed the man that city police chief Raymond Kelly said was acting in a "furtive" manner as he hurried away from the area.
He was "a white male in his 40s" and "seen shedding a dark colored shirt revealing a red one underneath," Kelly said.
He added that a tourist had contacted police to say he "may have got a picture of the individual" while he was filming a nearby mounted policeman.
While New York has been on a terrorist alert ever since the September 11, 2001 attacks, authorities have ruled out a major Islamist militant link to the bomb.
Mayor Michael Bloomberg said: "There is no evidence that this is tied in with Al-Qaeda or any other big terrorist organization."
Kelly also dismissed a claim of responsibility made over the Internet by the Pakistani group Tehreek-e-Taliban.
"I'm confident we'll find out who did it," Bloomberg said alongside the police officer who was first on the scene and whom the mayor treated to dinner in Times Square as a reward.
"This is the crossroads of the world. People feel safe in New York and they will continue to come here," Bloomberg said.
On a visit to the oil spill on Louisiana's coast, Obama said US security services had taken "every step necessary" in the hunt.
It remained unclear why the device -- comprised of fireworks, propane, gasoline and possibly fertilizer -- failed to detonate, despite smoldering after partly catching fire in the back of the Nissan.
Kelly said the bomb would have created a "significant fireball" in the teeming district. The car "would have at least have been cut in half."
The engine was still running and the emergency lights were blinking when the smoking car attracted a nearby street vendor. The vendor, a Vietnam War veteran, told police who quickly brought in the bomb squad.
"I did a lap around the vehicle. The inside was smoking," the first officer on the scene, Wayne Rhatigan, told the New York Daily News. "I smelled gunpowder and knew it might blow. I thought it might blow any second."
Kelly said the license plate on the utility vehicle belonged to a vehicle traced back to a Connecticut junkyard.
Officials said the attempted bombing was terrorism, but they were cautious about suggesting who might have been behind the attack, raising speculation that domestic militants were responsible.
Homeland Security Secretary Janet Napolitano said the FBI, the New York police and the government's Terrorism Task Force were probing a "potential terrorist attack."
There was no evidence of a broader plot, but law enforcement authorities had been alerted to "stay on their toes," she said.
The bomb, while threatening "mayhem," according to Kelly, was comprised of the kind of materials available from regular stores. Bloomberg called it "amateurish."
Kelly described a multi-layered device consisting of two alarm clocks as timers, a pot of fireworks as detonator, two canisters of gasoline, three propane gas tanks and a large box containing what was believed to be fertilizer.
The scare raised tensions across the United States where security forces have been on edge since a young Nigerian allegedly attempted to set off a bomb on a US airliner as it came in to land in Detroit, Michigan.
New York City police are on constant alert after a string of plots since the September 11, 2001 attacks.
In February, Afghan migrant and self-confessed Al-Qaeda agent Najibullah Zazi, 25, pleaded guilty to a plot to set off bombs in New York's subway system. He could be sentenced to life in prison.