The main culprits in a long-running corruption case involving Germany's Siemens group and Greek telecoms operator OTE were handed 15-year sentences by Greek judges on Monday, a legal source said.

Bavaria-based Siemens, whose links to Greece go back to the 19th century, had been suspected of greasing the palms of various officials to clinch one of the country's most lucrative contracts - a vast upgrade of the telephone network in the late 1990s.

A Greek appeals court last month announced 22 convictions in the case, including former Siemens executives and bankers.

On Monday, it handed down 15-year sentences to former local Siemens head Michalis Christoforakos, who fled to Germany over a decade ago, and to his deputy Christos Karavellas, who is also on the run, among others.

The trial opened in 2015 but the original investigation began over a decade ago. Ten defendants have since died.

A parliamentary committee in 2011 determined that inflated contract prices cost the country at least two billion euros ($2.2 billion at current rates) during the 1990s.