Telegraph UK

The device, which failed to detonate, was left near the offices of Viacom, which owns the irreverent cartoon series.

Last month postings on an Islamic website warned the creators of South Park - Matt Stone and Trey Parker - that they could face violent reprisals after an episode of the show featured Mohammed in a bear suit.

Images of the Prophet are strictly forbidden in Islam, and Comedy Central, which broadcasts South Park, has banned Stone and Parker from depicting Mohammed in the past. In 2006 the network stopped them from featuring Mohammed in an episode which followed worldwide protests over a caricature of the Prophet by a Danish cartoonist.

Detectives are also understood to be investigating striking similarities between the New York bomb and two car bombs planted by Islamic terrorists outside the Tiger Tiger nightclub in London in 2007.

In both cases, the devices comprised cylinders of propane gas and cans full of petrol intended to be ignited by electronic detonators.

David Paterson, the Governor of New York, described the Times Square incident as an "act of terrorism." He said: “Luckily, no one is hurt, and now the full attention of city, state and federal law enforcement will be turned to bringing the guilty party to justice in this act of terrorism.”

The bomb was left inside a dark green Nissan Pathfinder, left with its engine running and hazard lights flashing near the junction of 45th Street and Broadway.

A T-shirt vendor, who was a Vietnam veteran, alerted police when he noticed smoke coming out of it. Police hurriedly evacuated thousands of tourists and theatre-goers, including women in evening gowns, from the area on Broadway's busiest night of the week.

Heavily armed police and FBI agents were deployed on the empty streets as bomb disposal experts used a robot to break the windows on the vehicle and remove explosive material. The car contained three propane tanks, fireworks, two five gallon gasoline containers, two clocks with batteries, electrical wires and a 4ft by 2ft metal box.

New York Police Commissioner Ray Kelly said: "I think the intent was to cause a significant ball of fire."

New York Mayor Michael Bloomberg returned immediately to the city from a White House dinner. Speaking at the scene, he said: "We are very lucky. Thanks to alert New Yorkers and professional police officers, we avoided what could have been a very deadly event. The bomb squad confirmed that the suspicious vehicle did contain an explosive device. We have no idea who did this or why."

He added: "Terrorists who want to take our freedoms away from us focus on the symbol of those freedoms, and that's New York City."

Mr Bloomberg said the wiring of the bomb "looked amateurish" and it had used "consumer grade fireworks" that were easily obtainable.

The alarm was raised at 6.34pm (10.34pm GMT) and six minutes earlier a security camera had recorded the Nissan heading west on 45th Street. Police have also established that the car's plates, which were from Connecticut, were not the ones registered to it. They have already spoken to the owner of the plates who said he had taken them to a junkyard.

Mr Bloomberg said police had no reports of anyone being seen running away from the vehicle after abandoning it. Times Square is four miles north of the site where terrorists destroyed the World Trade Center on September 11, 2001. The area that was evacuated and shut down is one of the prime spots for Broadway shows, with seven theatres and shows including Billy Elliot.

Katy Neubauer, 46, who was shopping for souvenirs nearby, said there had been panic. She said: "It was a mass of people running away from the scene."Don Slovin, watching the police through the window of a shop a block away, said, "Of course it conjures up memories of 9/11."

President Barack Obama praised the quick response by the New York Police Department and said the federal government was prepared to provide support.

Bilal Abdulla, an NHS doctor from Iraq, was sentenced to life imprisonment in 2008 after being found guilty of plotting the failed Tiger Tiger bombings. His accomplice, Kafeel Ahmed, died after driving an explosive-packed Jeep into Glasgow Airport the day after the attempted bombings in London.