The US National Park Service has said engineers have discovered several additional cracks in the top portion of the Washington Monument.
The cracks were found during a day-long inspection of the interior of the monument.
A four-foot crack was discovered on Tuesday during an inspection of the exterior by helicopter, shortly after a 5.8-magnitude earthquake shook the nation's capital.
The monument is closed to visitors indefinitely.
Park service spokeswoman Carol Johnson could not say how many additional cracks were found but said engineers found three or four "significant" ones.
The park service is bringing in engineers from two firms with extensive experience investigating earthquake damage to conduct a more detailed inspection today.
Ms Johnson said it is likely that the additional cracks mean the monument will take longer to repair.