Socrates Kokkalis, the billionaire owner of Greece's biggest telecoms company and chairman of the Olympiakos football club, has been accused of working as an agent for the Stasi, the notorious secret police of the former East Germany.

He is the first Greek citizen to face a formal inquiry for spying against his own state.

Espionage is one of six serious offences for which Mr Kokkalis is being investigated; fraud, embezzlement and money-laundering are others. Under Greece's justice system, he was formally told of the charges against him last week. An investigating magistrate will now conduct the formal inquiry, and may call Mr Kokkalis for cross-examination before deciding whether the matter should go to trial.

Download the new Independent Premium app Sharing the full story, not just the headlines

Mr Kokkalis, who is worth an estimated $1.2bn (£863m), is the founder and chief of Intracom, a telecommunications equipment giant operating mainly in Greece and the Balkans, which lately signed a $100m deal with Raytheon of the US to build components for Patriot missiles.

The spy charges stem from evidence provided by the German authorities to the Athens prosecutor, Dimitris Papangelopoulos, which appears to show that Mr Kokkalis was hired by the Stasi to provide Western technological secrets. Despite his Greek citizenship, the 63-year-old businessman grew up in East Germany and was educated in Berlin and Moscow before starting his telecoms empire.

A 350-page file has been found in the Stasi archives referring to "Agent Rocco", who was recruited on 25 January 1963. A German parliamentary investigation identified the agent as Mr Kokkalis, saying that until his return to Greece in 1965 he regularly gave the Stasi information on his acquaintances and contacts.

A 1998 German parliamentary report recently made public said that between 1986 and 1991 Mr Kokkalis's account at Deutsche Handelsbank held $11m and DM1.7m (£530,000). These sums are alleged to have been used to bribe Greek officials to buy outdated East German equipment.

Mr Kokkalis denied the charges last week, saying he was the victim of a conspiracy by unnamed "political personalities" and newspapers.