WASHINGTON -- U.S. intelligence has picked up mention of possible terror attacks planned for New York, Washington, Boston and more broadly, the U.S. coastlines.

But federal law enforcement sources say there are doubts about the credibility of the threats. They also say those transmissions are not the reason why the government has raised the threat level to orange.

Authorities said they have nothing credible suggesting a time, method or target. But, they're concerned that the recent attacks overseas could mean al-Qaeda is setting its sights on the U.S. again.

The heightened alert status has heightened activity nationwide.

Police in California are working 12-hour shifts. National Guard troops in New York are protecting subways and bridges. In Washington, the Capitol Police SWAT team is ready to go on patrol.

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