PHILADELPHIA (CNN) — The U.S. Navy raised its threat level at a naval installation in Philadelphia Tuesday after receiving a “potentially credible threat,” a U.S. official said.

The Navy was informed by the FBI of the threat to potentially take place Tuesday. The threat level was raised to “Charlie” around 10:30 a.m., the official said.

Charlie level indicates imminent threat of terrorism, and is the second highest level. Under Charlie, non-essential workers would typically be sent home.

Local press reports said that Naval Station Activity Philadelphia, which supports logistics, supplies and other offices, was evacuated.

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