Putin said the Kremlin’s chief concerns remained unanswered – guarantees from the West that NATO would expand no further and that Ukraine would never be permitted to join.

The collective journey of Nevgen and Gonchar began in 2015, when the duo reconnected and founded MSQRD, a mobile app with a collection of masks and faces for the phones’ selfie cameras.

Moscow has repeatedly denied it has any intention of invading Ukraine but has held several rounds of talks with Western countries and NATO on its demand for “security guarantees“ that the Atlantic alliance will expand no further and Ukraine will never become a member.

In his third conversation with the Russian president in two months,  Biden said Washington would respond "decisively and impose swift and severe costs" if Russia moved into Ukraine.

Western estimates put at about 30,000 the number of Russian troops taking part in the exercises – along with most of the Belarusian army.