China's military condemned the transit of two German navy ships through the Taiwan Strait, saying it increased security risks and sent the "wrong" signal, adding that Chinese forces monitored and warned the vessels.
China, which claims democratically governed Taiwan as its own, says it alone exercises sovereignty and jurisdiction over the strait. Both the United States and Taiwan say the strait - a major trade route through which about half of global container ships pass - is an international waterway.
The People's Liberation Army's Eastern Theatre Command said the passage of the two ships - a frigate and a supply vessel - was "public hyping", and that its navy and air forces monitored and warned them throughout.
"The German side's behaviour increases security risks and sends the wrong signal. Troops in the theatre are on high alert at all times and will resolutely counter all threats and provocations," it said in a statement.
China's embassy in Germany said in a separate statement it had lodged "representations" with Berlin, saying Taiwan belonged to China, a position the democratically elected government in Taipei strongly rejects.
"The question of Taiwan is not a matter of 'freedom of navigation', but of China's sovereignty and territorial integrity," it said.
The Taiwan Strait is Chinese waters "and there are no so-called 'international waters' at all", the embassy added.
China urges Germany to avoid any "interference" that would jeopardise the healthy and stable development of bilateral relations, it added.
Taiwan's government says only the island's people can decide their future.
U.S. warships sail through the strait around once every two months, drawing the ire of Beijing, and some U.S. allies like Canada and Britain have also made occasional transits.
China, which has never renounced the use of force to bring Taiwan under its control, has over the past five years stepped up military activities around the island, including staging war games.
On Saturday, Taiwan's coast guard said it had again sent ships to monitor and warn away four Chinese maritime police vessels sailing in restricted waters near the Taiwan-controlled Kinmen islands, which sit right next to China's coast.
The Chinese ships have continued to provoke and damage peace in the strait, and the coast guard is determined to defend Taiwan's sovereignty upholding the principles of no provocation, no conflict and no show of weakness, it said.
Calls to China's defence ministry seeking comment went unanswered.
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