The White House and U.S. Capitol building were briefly put on lockdown Tuesday morning after a possible unidentified aircraft or other "anomaly" violated restricted airspace over Washington, sources said.

The incident caused an abrupt security situation, with jets being scrambled and officers warning people outside Capitol facilities to stay far away. The U.S. Secret Service said personnel at the White House were told to remain in place.

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But minutes later, the lockdown was lifted and both complexes were given the all-clear.

Fox News has learned that U.S. Capitol Police scrambled a helicopter, and the military scrambled fighter jets from Joint Base Andrews.

Law enforcement sources initially told Fox News the lockdown was triggered after an aircraft moving east violated restricted airspace. But Fox News is now told officials may have to go back and review the radar to determine what exactly prompted the scare, with sources saying they got "mixed signals at best" as to what the potential aircraft could have been.

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One source said they were never sure whether an actual aircraft was ever involved, while another told Fox News that radar was showing "different sectors" as to where the threat was coming from. One source said whatever they saw may have just been an “anomaly” or even “geese.”

Capitol Police sent a notification of a potential threat shortly after 8:30 a.m. People were allowed back in after about 30 minutes.

Fox News' John Roberts and The Associated Press contributed to this report.