Heavily-armed counter- terrorism forces were deployed in New York and high alert was sounded in the city and Washington after US officials warned of a new “credible” threat by al-Qaeda using car or truck bomb, timed with the 10th anniversary of the 9/11 attacks.

Additional forces were put on the streets with sniffer dogs as check points sprouted as the intelligence agencies came across the plot late Wednesday triggering a high level meeting at the White House.

President Barack Obama who was briefed on the threat directed the counter terrorism community to redouble their efforts in response to this credible but unconfirmed information.

“The President was briefed on this specific threat information this morning and has been updated on it throughout the day,” the official added.

“The United States government has already significantly enhanced its security posture in advance of the 9/11 anniversary to protect the country against possible terrorist threats,” the official said.

New York Mayor Michael Bloomberg disclosed that the terror threat to the city is “credible but not corroborated”.

The threat was received by the US intelligence agency on Wednesday and the officials have put a look out notice for three people, who entered the country last month by air travelling from Afghanistan via a third country.

Counter-terrorism officials were assessing the report and media reports said that authorities were contemplating raising the threat level in New York and Washington.

The agencies are also pursuing the leads overseas in an effort to unravel the plot, a statement by a spokesman for the department of Homeland Security said.

Further, a nationwide hunt has been launched for at least two missing rental trucks that remain untraceable from locations in Kansas City, Missouri, officials said.

The scare came days ahead of anniversary ceremonies for the 9/11 attacks when President Obama and his predecessor George W Bush are due in the city, along with large crowds.

On September 11, 2001, two hijacked planes hit New York’s World Trade Centre, turning the iconic twin towers to rubble, a third plane plowed into the Pentagon and the fourth plane crashed into a field in Pennsylvania.

Outlining the measures taken by the police department following the threat information, New York City Police Commissioner Raymond Kelly said more dog squads and police vehicles will be on patrol, increased bombs sweeps of parking garages and other locations would be undertaken.

Illegally parked cars would be also be increasingly towed.

According to the CNN the terror plot is believed to involve three individuals, including a US citizen.

US officials believed the threat was a vehicle laden with explosives, but “the intelligence picture is not completely formed,” the official said.

“Not enough is known about the potential operatives and their plotting,” the official was quoted as saying.

According to the NBC News the threat relates to car or truck bombs, while another news report said that the information originated in the tribal areas of Pakistan.

In New York, the City Mayor Michael Bloomberg at a news conference said that the city is raising bridge and tunnel security, setting up vehicle checkpoints and extending shifts for some police officers.