Federal prosecutors said the American citizen is suspected of offering access to intelligence when he worked for the US armed forces in Germany.
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Germany's Federal Prosecutor's Office said it had arrested a US national on suspicion of offering Chinese intelligence access to sensitive information.
The man, who was identified as Martin D, was arrested in the western city of Frankfurt.
Martin D worked for the US armed forces. He allegedly contacted Chinese government agencies in 2024 and offered them US military information.
"He had obtained the information in question during his work for the US armed forces" prosecutors said.
The suspect is expected to appear at a hearing in court later on Thursday.
The investigation was carried out in co-ordination with Germany's domestic intelligence agency, prosecutors said.
German prosecutors have arrested several people suspected of spying for China this year.
In April, an aide who worked for prominent far-right politician Maximilian Krah was arrested on suspicion of spying for China.
Before that, three German nationals were detained for arranging to transfer information on technology with potential military uses in a separate case.