China on Saturday accused Berlin of heightening security risks in the Taiwan Strait, a day after two German military vessels sailed through the sensitive waters.
German Defence Minister Boris Pistorius confirmed on Friday that the frigate Baden-Wuerttemberg and the supply vessel Frankfurt am Main sailed through the strait.
"The German side's behaviour increases security risks and sends incorrect signals," Chinese military spokesperson Li Xi said in a statement.
US military ships as well as those operated by other countries have often sailed through the sensitive waterway.
But the Baden-Wuerttemberg's voyage was the first time in more than two decades that Berlin's navy had done so, according to German media reports.
Beijing views Taiwan as a renegade province and claims jurisdiction over the body of water that separates the island from the Chinese mainland.
Germany and many other countries argue such voyages are usual, citing freedom of navigation.
China's Li said Saturday that the People's Liberation Army had sent sea and air forces to "monitor and warn off" the German vessels.
Beijing's troops in the area would "resolutely counter all threats and provocations", Li added.
The two vessels were headed from South Korea to the Philippines, German defence ministry officials said.
Pistorius said on Friday that the course charted by the vessels was "the shortest route".
"It is the safest route given the weather conditions. And these are international waters, so we are sailing through them."
- Freedom of navigation -
Though Taiwan has only a dozen diplomatic allies, it maintains strong partnerships with various Western democracies such as the United States, which is its biggest weapons supplier.
Beijing has in recent years engaged in an escalating campaign of intimidation against Taiwan, including through large-scale military exercises around the island.
The Chinese government warned this year that "Taiwan independence forces will be left with their heads broken and blood flowing".
Chinese state media reported in June that Beijing could impose the death penalty for "particularly serious" cases of what it views as separatism from Taiwan.
German Chancellor Olaf Scholz said on Friday when asked about the vessels that "there is not much to say... it's an international waterway".
Taiwan said earlier this week that it "welcomes and affirms Germany, along with the US, Canada and the Netherlands, for taking actions to demonstrate the legal status of the Taiwan Strait as international waters, while defending freedom of navigation and maintaining regional peace at the same time".