Nervous New York heads to work despite pram bomb warning

In Manhattan, police stood guard outside most subway entrances, some with sub-machine guns, while inside passengers with bags and briefcases were being asked to open them for inspection. Undercover detectives were deployed throughout the subway system, which carries 4.5 million people a day and serves 490 stations.

The authorities withheld information of a detailed threat, with particular reference to the possible detonation of a bomb in a baby-stroller, for several days, pending the arrest of terror suspects in Iraq, officials said. "We have done and will continue to do everything we can to protect this city," the Mayor, Michael Bloomberg, told reporters. "We will spare no resource, we will spare no expense." He did not change the city's colour-coded threat level, however.

In Washington, officials with the Department of Homeland Security played down the warning, saying the intelligence information was unconvincing.

Memories of what happened in London in July and Madrid last year have spurred city authorities to take no chances, however. The random inspection of bags in the subway was instituted for the first time in New York within days of the London bombings.

"The reality is we have to take it as a credible threat," Howard Safir, a former commissioner of police in New York, said yesterday. "We have to look at the history of Madrid and London. What would make us think we are not vulnerable to exactly the same kind of attack?"

Mr Bloomberg was among morning commuters yesterday and urged New Yorkers to continue using the subway. By most accounts, yesterday's commute was as busy as ever. "The cops have it under control," said Rob Johnson. "Hopefully, God's with me and I'll be OK," said Vinnie Stella, a computer consultant in downtown Manhattan.

In crowded carriages, however, there was no one who had not at least glimpsed the day's headlines. And they were not reassuring. "Subway Bomb Plot", blared the New York Post, while the Daily News shouted: "Bombs In Strollers".

Mr Bloomberg defended the three-day delay in going public with the new threat, saying that it allowed the police department to complete preventive actions beyond the glare of the media.

"There were operations taking place that we thought were in the interest of ending the threat, and releasing the information early could have jeopardised the lives of those conducting those operations," he said.