Mass Transit Security Warning Issued

(CBS/AP)  U.S. mass transit systems should remain alert against possible terror attacks, the Homeland Security Department said in a new warning that highlighted suspicious activity at unnamed European subway stations last fall.

Homeland Security spokesman Russ Knocke said Wednesday there is no specific or credible intelligence to indicate U.S. transit systems are being targeted, CBS News correspondent Bob Orr reported, and he described the notice, sent Tuesday, as a routine reminder for transit authority operators, state security advisers and police to remain on guard. The department decided to share the information out of an abundance of caution, Orr noted.

In Chicago, transit authority spokeswoman Sheila Gregory said the nation's second largest transit system had not received any information or warning from Homeland Security regarding suspicious activity at European subway stations.

Joe Pesaturo, a spokesman for the Boston area transit authority, said the agency is already on alert.

"We have received the memo and we are continuing to operate under the procedures we have in place for the elevated threat level," he said.

The notice said a foreign man was arrested in November in an unnamed European city after videotaping the interior and exterior of several subway cars and stations, including trash cans and stairwells. The man taped nearly 17 minutes of subway pictures, the notice said, but "the camera contained no footage of tourist sites."

Three other people were later arrested for similar activity, including two in the last four months, the notice said.

The incidents "prove indications of continued terrorist interest in mass transit systems as targets, and potentially useful insights of the terrorists' surveillance techniques," said the notice, a copy of which was read to The Associated Press.

It added: "DHS has no credible or specific intelligence regarding active plots targeting U.S. mass transit systems."

Knocke said Homeland Security has no immediate plans to raise the nation's terror threat alert level. It was not immediately clear why the arrests months ago prompted the new notice.

However, Knocke said it was not connected to Wednesday's sentencing verdict of al Qaeda conspirator Zacarias Moussaoui, who was sentenced to life in prison.

An estimated 32 million Americans ride mass transit daily. A spokeswoman for the Washington Metropolitan Transit Authority in the nation's capital the new notice did not spark any alarms, but "we constantly remain vigilant."

"It's not unusual for people to take pictures of the Metro system, and we keep an eye out of there's anything unusual about them," said Metro spokeswoman Candace Smith.

A spokeswoman for the American Public Transportation Association, which represents the nation's subway, rail and bus systems, did not have an immediate comment.

U.S. mass transit systems were put on high alert for 36 days last summer after London's deadly July 7 bombings on three subway trains and a bus. Those attacks killed 52 people and the four bombers.

Two years ago, commuter train bombings in Madrid killed 191 people in attacks that were initially claimed by al Qaeda. Investigators have since said Osama bin Laden's group gave no logistical or financial support to the bombers.