Greek Prime Minister Alexis Tsipras listens during his meeting with Russian President Vladimir Putin (not pictured) in Moscow, Russia December 7, 2018. REUTERS/Maxim Shemetov/Pool

MOSCOW (Reuters) - Greek Prime Minister Alexis Tsipras said on Friday that he had expressed his concern during talks in Moscow with Russian President Vladimir Putin at Turkey buying weapons from Russia, TASS news agency reported.

Turkey has purchased S-400 surface-to-air missile systems from Russia in a deal that has unnerved the United States and Turkey’s NATO allies.