New Yorkers went about their business under tightened security on Sunday, the day intelligence officials said the city's subway might become target of terrorist attack, as officials are still trying to corroborate the alleged "specific" threat to the city's transit system.

Beefed-up security measures that began on Thursday continued throughout the city, with troops in combat gear patrolling transportation hubs, such as Penn Station, Grand Central Station and the Port Authority bus terminal.

Increased police presence was seen even in smaller subway stations and random bag search was more frequent. According to police, reports of suspicious packages had more than doubled in the pat few days, but no dangerous items have been found so far.

Despite doubts by some federal officials that the threat was not credible, New York Mayor Michael Bloomberg and Police Commissioner Ray Kelly told the public that they are the one in charge of keeping New Yorkers safe.

"They have their views, but we have to make the decision," said the mayor."��Its easy to analyze and say this is possible, that's possible, but when it gets down to the level of a city, we've got to make a decision."

Kelly told Fox News Sunday television program that New York authorities "have a responsibility to the 8.1 million people that live in this city."

"We're in a city that's been attacked twice successfully by terrorists, almost 3,000 people killed here four years ago, so we might have a different set of priorities than other folks," he said.

On Thursday, the city authorities went public with the threat that terrorists planned to use timed or remote-controlled explosives hidden in briefcases, suitcases, and under strollers on or around Sunday.

Some federal officials have been skeptical about the threat since it was announced Thursday, but they appeared to be softening their assessment of the possible danger.

In a statement issued Saturday by the Department of Homeland Security, its director Michael Chertoff said he respects mayor Bloomberg's judgment and expressed the belief that the security precautions being taken by New York city are "absolutely an appropriate response while this and other intelligence information continued to be examined and analyzed."

So far three suspects have been arrested in connection with the alleged plot, all of them in Iraq. Sources say authorities are investigating whether a fourth man traveled to New York as part of the scheme.

Police Commissioner Kelly said New York would remain on heightened alert until intelligence authorities in Iraq could pin down the credibility of the current threat. Tightened security in transit system would be in force again next week, and the situation would be monitored "on an hourly basis," he added.

Source: Xinhua