China has been caught on camera building a new counter-stealth radar system on a disputed reef in the South China Sea, sending fears spiralling over its spying in the region.
Fresh research from the Royal Institute of International Affairs suggests Beijing is upgrading its outpost on Triton Island, on the southwest corner of the Paracel archipelago in the South China Sea.
It comes amid warnings that a submarine arms race is ramping up between China and the West - with Beijing looking on track to have a new generation of nuclear-powered and armed submarines in operation by the end of the decade.
China controversially claims almost all the South China Sea, including areas claimed by Brunei, Malaysia, the Philippines and Vietnam.
Xi Jinping's forces have been building up spy capabilities on the contested islands
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Triton is claimed by China, Taiwan and Vietnam
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He said: "By constraining the US ability to operate stealth aircraft, and threaten stealth aircraft, these capabilities in the South China Sea send a powerful signal to US allies and partners in the region that the US advanced technologies may not be able to stand up to the PLA (People’s Liberation Army)."
Any construction on Triton is likely to be of concern to Vietnamese officials - and according to Chatham House’s analysis, the intelligence lookouts on Triton would "significantly diminish" Vietnam’s capacity to operate unmolested by China in the area.
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 US.
The satellite images show a dense build-up of Chinese spy tech
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Closer photos of the military buildings on Triton
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And, like its Nato commitments, the US is treaty-bound to defend the Philippines if it is attacked.
China has also recently staged so-called war games around Taiwan - in which it simulated attacks and deployment of ships and aircraft, drawing condemnation from the Taiwanese government and the US alike.
A spokesman for the Chinese state security ministry said: "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 spokesman did not specify where the devices were found.