The bidders are Greek contractor GEK Terna with France's Vinci and Siemens; J&P Avax with Italy's Ghella and France's Alstom Transport; and Greek construction firm Aktor with Spain's Ansaldo and Hitachi Rail Italy;

The contractors have until Dec. 10 to submit their technical and financial offers, Attiko Metro said in a statement.

Construction of the 13 km (8 miles) expansion - which will be co-financed by European funds and loans by the European Investment Bank - is expected to begin in 2019 and will be completed within eight years.

(Reporting by Angeliki Koutantou; Editing by Mark Potter)