The US National Park Service said engineers have discovered several additional cracks in the top portion of the Washington Monument.
The "significant" cracks were found during a day-long inspection of the interior.
A 4ft-crack was discovered on Tuesday during an inspection of the exterior by helicopter, shortly after a 5.8-magnitude earthquake shook the capital.
The monument is closed to visitors indefinitely while engineers with quake damage experience are examining the cracks.
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