China warns of deep-sea spying devices, underwater 'lighthouses' that guide foreign submarines

The ministry said it had uncovered devices that had been hidden on the ocean floor and were sending back information that could "pre-set the field for battle," in an article on its official WeChat account, China's most popular social media app.

Recent sea and air confrontations in the South China Sea between China and the Philippines over competing territorial claims in the highly strategic waterway have raised the risk of an escalation that could eventually involve the U.S., which is treaty-bound to defend the Philippines if it is attacked.

China has also recently staged war games around Taiwan in which it simulated attacks and deployment of ships and aircraft, drawing condemnation from the democratically governed island's government and the United States.

"National security forces have seized a variety of special technical devices used for spying on marine information and data, hidden in the vastness of the sea," the state security ministry said, without specifying where the devices were found.

"Some act as 'secret agents,' drifting and floating with the waves, monitoring the situation in our territorial waters in real time. Some act as underwater 'lighthouses,' indicating the direction for foreign submarines that have invaded our waters."

China claims sovereignty over nearly all the South China Sea, including areas claimed by Brunei, Malaysia, the Philippines and Vietnam.

Beijing has also said it will never renounce the use of force over Taiwan, which rejects China's sovereignty claims and says only the island's people can decide their future.

A submarine arms race is intensifying between China and the United States and its allies, analysts say, with Beijing on track to have a new generation of nuclear-powered and -armed submarines in operation by the end of the decade.

"Facing a serious and complicated covert struggle for deep-sea security and the real threat of foreign espionage and intelligence agencies... (the ministry) will firmly defend China's sovereignty, security and development interests and contribute to the construction of a strong maritime nation," the ministry said.