Construction of China's first full-size aircraft carrier is well underway, according to satellite images obtained and analyzed by a U.S. think tank.

The images from April, provided to Reuters by the Center for Strategic and International Studies (CSIS) in Washington, reveal considerable recent activity during the last six months on a large vessel at the Jiangnan shipyard outside Shanghai.

China has not formally confirmed it is building a third carrier, despite recent hints in state media, and the timing and extent of its carrier program remain state secrets.