NEW YORK (Reuters) - New York City's subway system is under its most specific threat of a terrorist attack ever, Mayor Michael Bloomberg said on Thursday, saying the threat came from overseas but had already been partially thwarted.

Bloomberg told reporters the FBI had notified him in recent days about "a specific threat to our subway system" but had not told the public until now because law enforcement officials were trying to head off the attack.

The city is stepping up surveillance of the system, the largest in the United States.

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A friend of a colleague who works in DHS told him not to take NY subways in next few days.

just informing..