China has started construction of the world’s biggest hydroelectric dam, a project that’s set to be far larger than the Three Gorges Dam — already the world’s biggest single source of green power — and more expensive than the International Space Station.

The project on a river that runs through Tibet and India downstream could dwarf the Three Gorges Dam when completed.

China on Wednesday said the construction of what will become the world’s largest hydropower project in the southern Tibet region is “fully” within its “sovereignty.” Responding to concerns raised by India and Bangladesh, Chinese Foreign Ministry spokesman Guo Jiakun said the project will not “adversely” affect downstream countries.