Active Shooter' Scare at Joint Base Andrews Sparks Lockdown (UPDATED)

UPDATE: Senior law enforcement officials confirmed there was never an “active shooter” at Joint Base Andrews on Thursday, NBC News’ Pete Williams reported.

Williams said the officials told him the confusion stemmed from a planned "active shooter" drill on Thursday morning.

"There were two personal walking across the base carrying rifles…someone in the medical center on the third floor looking out the window saw that and phoned in that there was a shooter on the base," he reported.

Sources: No active shooter at Joint Base Andrews https://t.co/DcKxp2ddzY

— MSNBC (@MSNBC) June 30, 2016

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Joint Base Andrews in Camp Springs, Maryland, is on lockdown after a "report of an active shooter."

The base advised all personnel to “shelter in place."

As of 9:36 a.m. ET, the incident was described as "ongoing."

Homeland Security Secretary Jeh Johnson addressed the situation on social media, calling the incident an "unfolding situation."

NBC Washington reported that there may have been a planned active shooter exercise on Thursday.

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