Germany's ambassador to Beijing said Thursday she had been summoned by Chinese authorities over the arrests of four Germans on suspicion of spying for China.

"After four Germans were arrested this week for allegedly spying for Chinese secret services, I was summoned to the (ministry of foreign affairs) today," Patricia Flor said on X, formerly Twitter, adding that it was "a quite telling move".

Three people arrested in western Germany on Monday faced accusations of passing information on maritime technology to China.

And on Tuesday, an assistant to a German member of the European Parliament was detained on the suspicion he was sharing details of proceedings in the assembly with Beijing and spying on Chinese opposition figures in Germany.

Flor said her meeting in the foreign ministry in Beijing was "a good opportunity to explain a few things".

"We do not tolerate espionage in Germany, regardless of which country it comes from," Flor said.

Germany would "protect our democracy and our constitutional state" against espionage attempts, the ambassador said.

The arrests deepened concerns about the extent of Chinese espionage in Germany, and prompted an angry response from Beijing.

Chancellor Olaf Scholz, who visited Beijing and held talks with Chinese leader Xi Jinping just a week ago, said the spying allegations concerning the far-right MEP were "very worrying" and would be investigated.

The Chinese foreign ministry said Tuesday the claims were an attempt to "smear and suppress China".