NEW YORK - Authorities stepped up mass transit security Thursday after receiving a credible threat that the city's subway system could be the target of a terrorist attack in coming days.
Mayor Michael Bloomberg and Police Commissioner Raymond Kelly said at a news conference the threat originated overseas. Bloomberg said it was the most specific threat New York officials had received to date. He said no one in New York has been arrested.
A law enforcement official, who spoke on condition of anonymity, said the threat is "specific to place, time and method" and involves a bombing.
"We have done and will continue to do everything we can to protect this city," Bloomberg said. "We will spare no resource, we will spare no expense. We have increased our police presence on our subways."
Kelly urged the public to report suspicious people or activities. Police planned to start looking through bags, briefcases, baby strollers and luggage in a large-scale search of the city's mass transit system
"We have never had before a specific threat to our subway system," Bloomberg said. "Its importance was enhanced above the normal level by the detail that was available to us from intelligence sources."
New York's security level remained at orange, the second-highest. It has been at that level since Sept. 11.
An estimated 4.5 million passengers ride the New York subway on an average weekday. The system has more than 468 subway stations.