Russian monitors will fly over Greece and the United States as part of Russia’s Treaty on Open Skies responsibilities, according to the statement published by Russian Defense Ministry on Monday.

“The flight [over Greece] will depart at some point on September 26-30 from Nea Anchialos “open skies” airport,” Sergei Ryzhkov, head of the Russian Defense Ministry’s Nuclear Risk Reduction Center, said, as quoted in the statement.

According to Ryzhkov, Russian observes will take off from Travis airport in California for their US flight that will take place sometime in the last week of September.

The Treaty on Open Skies entered into force in 2002, providing for unarmed aerial surveillance flights between member states. Out of 34 states that have ratified the agreement, 27 are Organization for Security and Co-operation in Europe (OSCE) members.