The 54-year-old officer, who was not named but was serving in a unit in the Athens region, appeared before military judicial authorities who ordered his detention, said the ministry source, who spoke on condition of anonymity.

The Greek press agency (ANA) said the man would be questioned by a military prosecutor on Tuesday.

The officer was arrested on Thursday. A brief Greek general staff statement said there was "clear evidence of criminal acts falling under the military penal code, namely the collection and transmission of classified military information to third parties, with the risk of harming national interests."

A military source, speaking on condition of anonymity, said the officer was part of an air force brigade who had access to sensitive national security details, including on technology.

The source and Greek media said the officer provided the information to contacts in China.