Michael Bloomberg spoke after police dismissed claims by a Pakistani Taliban group that it was responsible.

Investigators are hunting a middle-aged white man seen removing his shirt near the scene at Times Square on Saturday evening and stuffing it into a bag.

President Barack Obama has vowed the US will track down the perpetrators.

Investigators have been gathering evidence from the Nissan Pathfinder in which the homemade petrol and propane bomb was found.

Behaving 'furtively'
The engine was still running with hazard lights flashing when the SUV, emitting smoke, attracted the attention of a street vendor.

Police evacuated part of the bustling entertainment district and shut subway lines, while a controlled explosion was carried out.

New York City Police Commissioner Raymond Kelly said on Sunday the bomb was crude, but could have sparked a “significant fireball”.

Another component of the device was a rifle cabinet packed with more than 100lb (45kg) of fertilizer, although police said it was not of a type volatile enough to explode.

Commissioner Kelly said they were looking for an unidentified white man, thought to be in his 40s, who was spotted behaving “furtively” nearby.

CCTV captured the suspect walking down an alley and changing a shirt, while looking back in the direction of the smoking SUV.

Home video
Police are also examining a home video taken by a tourist of a man seen near the car.

There is no evidence this is tied in with al-Qaeda or any other big terrorist organisation

Mayor Michael Bloomberg
Detectives have established that the car's registration plates do not match up with the Nissan.

They belonged to a car owner in the state of Connecticut, who told officers he had sent the plates to a scrap-yard.

A Pakistani Taliban group claimed in a one-minute internet video that it was behind the failed attack.

Tehreek-e-Taliban said the bomb was revenge for the deaths of its leader and the leader of al-Qaeda in Iraq.

But the police commissioner and the mayor cast doubt on the claim.

“There is no evidence that this is tied in with al-Qaeda or any other big terrorist organisation,” Mr Bloomberg said.

The mayor earlier told reporters New York had avoided what could have been “a very deadly event”.

'Pop, pop, pop'
US Homeland Security Chief Janet Napolitano has said there was so far no evidence that it was more than a “one-off event”, but added it was “a potential terrorist attack”.