Construction of a helicopter base on Nanji Island was observed by a commercial spy satellite in October. The island is off the coast of Zhejiang province—some 186 miles northwest of the Senkakus, a group of resource-rich islets China calls the Diaoyu Islands.

The imagery, obtained from the Airbus Defense and Space-owned Pleaides satellite, reveals China is constructing an airfield with 10 landing pads for helicopters on Nanji Island.

Military analysts said the new military base appears to be preparation by the Chinese People’s Liberation Army for an attack or seizure of the Senkakus.

“China’s new heli-base on Nanji Island demonstrates that the PLA is preparing for an offensive military operation against the Senkaku/Daiyoutai Islands,” said Rick Fisher, a senior fellow with the International Assessment and Strategy Center.