"An evaluation of the (international) press coverage has given cause for a preliminary investigation," a spokesman for Bochum's prosecutors office, which specialises in financial corruption cases, told AFP without giving more details.

On Monday, business newspaper Handelsblatt reported that German authorities are investigating the large military contract concerning the sale of German-built submarines, at the request of authorities in Israel who have been investigating the matter since 2016.

The case, known as "3000", focuses on suspicion of corruption surrounding the sale of three 'Dolphin' class submarines and four 'Saar 6' naval vessels, built by German industrial giant Thyssenkrupp for a reported sum of around two billion dollars.

Last week, Michael Ganor, a former Thyssenkrupp employee, was arrested in Israel after informing police of his intention to "change the version he gave during the investigation" into corruption suspicions around the purchase of the German submarines.

The scandal threatens to drag in Netanyahu as several of his relatives and close affiliates have been implicated.

Police said in November there was evidence to press charges against a number of suspects, including Netanyahu's cousin and lawyer David Shimron.

Netanyahu was questioned as a witness in the case and was not considered a suspect.

His main political rival, Benny Gantz, a former chief of staff of the Israel Defense Forces, last week called for a full investigation into the affair.