Personnel from the US, Estonia and Lithuania observed military infrastructure in Russia and Belarus under the Open Skies Treaty.
The observation flights on February 19 and 20 recorded military installations in the Western Military District of Russia and in Belarus, according to BNS quoted by Estonia's ERR News.
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"Flights under the Open Skies Treaty [...] give us a better possibility to observe developments in the eastern neighbor's military infrastructure," said Peeter Kõiv from the Estonian defence forces.
The flight followed the route Kubinka in western Russia down to Belarus and onward to Russia's exclave of Kaliningrad, with a separate flight recording installations in Kaliningrad.
Established on March 24, 1992, the Open Skies Treaty permits partaking countries to conduct short-notice, unarmed, reconnaissance flights over the others' entire territories to collect data on military forces and activities, according to the Arms Control Association NGO in the US.
The treaty entered into force on January 1, 2002, and includes 34 countries.