Prosecutors have arrested a man working for a far-right politician on suspicion of spying for China.
They have identified the man as Jian G, 43, named by German media as an assistant to AfD MEP and European election candidate Maximilian Krah.
Prosecutors say he was arrested in the eastern city of Dresden. They allege he passed information about the European Parliament to Chinese intelligence.
Jian G is also suspected of spying on Chinese opposition figures in Germany.
A spokesman for the AfD party (Alternative for Germany) said the arrest was "very disturbing" and that they awaited further investigation from the public prosecutor.
Interior Minister Nancy Faeser said the allegations were extremely serious: "If it is confirmed that someone spied for China in the European Parliament, this is an attack from within on European democracy."
China's foreign affairs ministry rejected the arrest as speculation designed "to smear and suppress China".
Prosecutors said Jian G had worked since 2019 "for a member of the European Parliament". They did not name Mr Krah, who is the AfD's lead candidate in the European Elections which take place in the EU's 27 member states from 6-9 June.
The BBC has approached Mr Krah for comment.
Jian G is due to go before an investigating judge later on Tuesday.
His detention comes a day after two men and a woman were arrested on suspicion of spying for China, by allegedly obtaining information in Germany about military technology for China. The latest case is not believed to be linked.
The main suspect in that case is alleged to have operated a front company working with German research organisations while spying for the Chinese Ministry of State Security (MSS).
Thomas R is alleged to have obtained "innovative technologies for military use" on behalf of an MSS employee.
German Chancellor Olaf Scholz returned days ago from an important visit to Beijing where he held talks with President Xi Jinping on issues including Russia's war in Ukraine.