ATHENS - Greece is in advanced discussions with China’s Cosco to boost their cooperation in the country’s biggest port Piraeus , the Greek defence minister said on Friday. Cosco, which currently manages two container piers at Piraeus Port, is also interested in acquiring a majority stake. Athens has put the port up for sale. “We are in very advanced talks to expand this cooperation very soon in relation with the inclusion of a railway network as well,” Defence Minister Panos Kammenos told an economic conference in Athens. Kammenos is the leader of the junior partner in the country’s leftist-led government. Greece unblocked the sale of a 51 percent stake in Piraeus port and has invited Cosco and two other shortlisted investors to submit binding bids by September.