Turkish President Tayyip Erdogan speaks with his Russian counterpart Vladimir Putin during a meeting at the Presidential Palace in Ankara, Turkey April 3, 2018. Sputnik/Mikhail Klimentyev/Kremlin via REUTERS

MOSCOW (Reuters) - Russian President Vladimir Putin said on Tuesday that a contract to supply Russian S-400 missile systems to Turkey is a priority in military cooperation between Moscow and Ankara, Russian state-run RIA news agency reported.