BBC News Online: World: Americas

US alert linked to Bin Laden

Mr Ridge said there was a convergence of information

"You can fairly assume this is tied in, in some way, with Bin Laden or al-Qaeda," Mr Ridge told reporters.

The warning came as New York City confirmed its first case of inhalation anthrax - the most dangerous form of the disease.

A 61-year-old woman who works at the Manhattan Eye, Ear and Throat hospital is in "very serious" condition after apparently contracting the disease last week.

Investigation

New York Mayor Rudolph Giuliani said on Tuesday that more than 300 people who worked with the woman are being tested for the disease and interviewed as to where it could have come from.

The hospital has been closed temporarily.

Mr Ridge said that the government had decided to issue a warning - the second of its kind in less than a month - because of "a convergence of credible sources, more than usual".

He said that the 11 September suicide attacks on New York and Washington had led to unprecedented international co-operation among intelligence agencies.

He said that Americans should not be dissuaded from going about their business, but should be alert to possible threats.

"Continue to live your lives, continue to be America, but be aware, be alert, be on guard," he said.

The BBC's Tim Franks in Washington says the administration is taking a calculated risk, weighing the danger of causing undue panic against the benefit of heading off a possible attack.