China’s latest nuclear submarine sank during its construction earlier this year, senior US defense officials said on Thursday.

Satellite images from June showed cranes at the Wuchang shipyard where the Zhou-class attack submarine would have been docked.

These images indicate that the vessel likely sank between May and June, US officials told news agencies including the Associated Press and Reuters.

China has not confirmed the current status of the submarine.

Reports of a submarine sinking during construction could be a potential setback for China as it continues to expand its naval capacity.

“We are not familiar with the situation you mentioned and currently have no information to provide,” a Chinese embassy spokesperson in Washington said.

A US official, who spoke on the condition of anonymity, told Reuters it was “not surprising” that China’s navy would hide the sinking of the submarine.

“In addition to the obvious questions about training standards and equipment quality, the incident raises deeper questions about the PLA’s internal accountability and oversight of China’s defense industry — which has long been plagued by corruption,” they added, using the acronym for the People’s Liberation Army.