This aerial photo taken on January 2, 2017 shows a Chinese navy formation, including the aircraft carrier Liaoning (C), during military drills in the South China Sea.

The head of the U.S. Navy has warned China that hostile behavior from its coast guard and fishing boats will not be treated any differently from the Chinese navy, the Financial Times reported on Sunday.

In an interview with the FT, Admiral John Richardson said he told Chinese vice-admiral Shen Jinlong in January that Washington will respond to aggressive acts by these non-naval ships the same way it has with the People's Liberation Army Navy.

That's because non-naval ships have been used to help Beijing stake its claims in the disputed South China Sea, the London-based newspaper reported Richardson as saying.

"I made it very clear that the U.S. navy will not be coerced and will continue to conduct routine and lawful operations around the world," Richardson told the newspaper.

The warning from the U.S. Navy comes as China increasingly relies on its coast guard and maritime militia — or marine industry workers trained alongside its navy — to expand its military presence in the region.