UPDATED 09/09/11 6:07 a.m.

CHICAGO (CBS) – As the 10th anniversary of the Sept. 11 attacks approaches this coming Sunday, the country is now facing a credible terror threat.

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Authorities say the threat was specific enough that it could not be ignored.

As CBS 2’s Susanna Song reports, it is important to stress there is no specific or credible threat to Chicago at this time.

U.S. officials said Thursday they were investigating a detailed al Queda car-bomb plot aimed at bridges or tunnels in New York City or Washington.

The threat was received Wednesday night. The report is unconfirmed, but a number of officials say there are enough elements lined up to have them take it seriously.

Sources tell CBS News the threat came from Pakistan, home to the Pakistani Taliban, the same group behind the failed Times Square bombing attempt. Sources also tell CBS News the operatives may be acting on Osama bin Laden’s wishes to attack on the anniversary of 9/11.

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“Now these are things al-Qaeda likes to do, anyway,” DePaul University terrorism expert Tom Mockaitis tells CBS 2’s Pamela Jones. “I don’t think it would have been taken as seriously were it not for the timing.”

Mockaitis added that it is important not to overreact.

“I would urge people not to change their travel plans; not to change any of their plans for the weekend, because all that does is give the terrorists what they want,” he said. “If, in fact, we get more information — the Department of Homeland Security gets more information about what’s going down, they’re going to let people know, and there might be some more specific instruction as to what to do. At this point, it doesn’t seem to be likely.”

New York City had already been in a heightened state of readiness in anticipation of the 9/11 anniversary.

Meanwhile, Chicago emergency officials announced that they are being vigilant and urged residents follow suit.

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“The City of Chicago has been in contact with our state and federal partners. While there is no credible threat to the City at this time, we remain vigilant. We encourage residents to also remain alert, and call 911 if you witness any suspicious or unusual activity,” a news release said.