New York - US investigators combed evidence on Sunday for clues to the perpetrator who left a crude but potentially deadly car bomb smoking in New York's packed Times Square.

Officials remained silent on who they thought was behind the attempted bombing late on Saturday.

An internet video purportedly from Pakistani Taliban group, Tarik-e-Taliban, claimed responsibility, the US monitoring service Site said.

Posted on YouTube, the video said the attempted bombing was to avenge the recent killing of two top al-Qaeda leaders in Iraq and US drone strikes in Pakistan, Site said. The claim could not be verified immediately.

New York's security services had a wealth of evidence to work from, starting with the green Nissan Pathfinder found packed with propane gas canisters, gasoline, fireworks, wires and two clocks.

Licence plates on the car were registered to a different vehicle, police said, while identification marks on the Nissan had been erased.

Surveillance cameras

Times Square - one of the city's top tourist attractions and teeming with thousands of tourists and theatre-goers at the time of the incident - has many surveillance cameras, giving police another strong line of investigation.

The bomb was described by New York Mayor Michael Bloomberg as an "amateurish" but potentially deadly attempt to create a fireball.

A sharp-eyed T-shirt vendor and Vietnam War veteran first saw smoke coming from the vehicle and alerted police, who quickly realised this was no ordinary car fire and brought in the bomb squad.

"We are very lucky... (to) avoid what could have been a very deadly event," Bloomberg told an impromptu news conference on Sunday.

Officials said it was the work of terrorists, but remained cautious, declining to say whether the culprit might be US-based or linked to al-Qaeda or another foreign group.

Homeland Security Secretary Janet Napolitano said the FBI, the New York police and the government's Terrorism Task Force were probing the "potential terrorist attack".

Asked whether fingerprints had been taken that could be helpful, Napolitano told CNN: "There is all that - forensics about the vehicle, about the tanks, the propane inside.

"There are forensics in terms of video or possible video that might exist. There is a lot of evidence being tracked down by a lot of people right now."

No evidence of broader plot

So far there was no evidence of a broader plot, but law enforcement authorities had been alerted to "stay on their toes", she said.

Police were checking other cameras that may have captured the vehicle, and more importantly, "people seen driving or leaving the vehicle", New York Police Commissioner Raymond Kelly said.

Bloomberg said it was not known "who drove the car.... We have no idea who did this or why".

Governor David Patterson said New Yorkers owed a debt of gratitude to the police and the vigilant T-shirt vendor, who told police officer Duane Rhatigan he became concerned after seeing smoke coming out from the Nissan SUV.

"I did a lap around the vehicle. The inside was smoking," Rhatigan later told the New York Daily News. "I smelled gunpowder and knew it might blow. I thought it might blow any second."

Times Square, one of the busiest areas of New York, was locked down for hours before being re-opened as security forces launched a manhunt for the Nissan's driver.

Broadway theatres, which faced disruptions on Saturday, were running normally on Sunday, but the scare raised tensions across the US 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 Denver.

Obama briefed

President Barack Obama had been briefed on the latest incident and "commended the quick action by the NYPD", White House press secretary Robert Gibbs said.

John Brennan, the president's deputy national security adviser, is working with the NYPD and others and will continue to keep the president up to date on the investigation, the White House said.

New York City police are on constant alert after a string of terrorist plots and alleged plots in the wake of the September 11 2001 attacks.

In December they closed Times Square while inspecting a van at first feared to contain a bomb, but which turned out to be carrying nothing dangerous.

In February, Afghan immigrant 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.

Last year, four New Yorkers went on trial in an alleged plot to bomb a synagogue in the city and shoot down military planes.

Nearly 3 000 people died in the 9/11 attacks when airliners hijacked by Islamist suicide squads slammed into the Twin Towers of the World Trade Centre in Manhattan, demolishing both sky scrapers.

- AFP