A Chinese nuclear-powered attack submarine sank in its dock earlier this year while under construction, according to US defense officials. The incident likely occurred between May and June. Satellite images from June show salvage cranes at the Wuhan berth where the submarine was previously seen. Beijing has not confirmed the reports. It is unclear if the submarine was carrying nuclear fuel. The BBC reviewed satellite images but could not conclusively identify the submarine. A Chinese Foreign Ministry spokesperson did not provide information when asked about the incident.