The al-Qaeda activist named by US officials as the source of information that led to the heightened terrorist alerts in New York and Washington was working undercover for Pakistani intelligence, report agencies.

The disclosure led to the collapse of the sting operation and the removal of the suspect to a 'safe' place by the Pakistan authorities.

Mohammad Naeen Noor Khan, a 25 year old computer engineer, was arrested at Lahore airport July 13.

Khan's arrest was kept secret because Pakistani intelligence 'coaxed' him to take part in a sting operation, and send out messages to several cells in order to track them down.

Computer disks recovered from him revealed that he was responsible for transmitting instructions from Al Qaeda leader Osama bin Laden to his operatives worldwide.

Apart from contacts of several al Qaeda cells and operatives, the disks had detailed plans and information about several US and British targets, including financial centers and other public buildings.

Though the list was compiled in 2001, Washington upgraded the terrorist alert around several sites mentioned, including the New York Stock Exchange and the headquarters of several financial institutions like Citigroup, insurance giant Prudential Financial, and the IMF and World Bank buildings in Washington. Detailed plans of London's Heathrow airport were also on the list.

Khan's evidence also led to the capture of at several terrorists in Pakistan, the UK, Saudi Arabia and the UAE. This included Ahmed Khalfan Ghailani, a Tanzanian wanted in the deadly bombings of US embassies in east Africa in 1998. In the UK, the arrest of 13 terrorist suspects, including the leader of a British terrorist cell, were also said to be on the basis of evidence provided by Khan.

Pakistan widens net for Al Qaeda militants

But in Washington, US officials justifying the heightened security disclosed his name at a 'background briefing' for journalists last week, leading to the abortion of the operation and the removal of Khan to a safer place by the Pakistani authorities.

"The Pakistani interior minister, Faisal Hayat, as well as the British home secretary, David Blunkett, have expressed displeasure in fairly severe terms that Khan's name was released, because they were trying to track down other contacts of his," Sen. Charles Schumer told CNN.

"We did not, of course, publicly disclose his name," demurred US national security adviser Condoleezza Rice on a talk show Sunday. It was given strictly "on background."

America's war on terror: complete coverage/ More reports from Pakistan