But many Allies will worry that appointing a figure from the former Warsaw Pact, from a country that agreed to deploy American anti-missile defences on its soil, might antagonise Russia.

Moscow has threatened to target its missiles at former Warsaw Pact countries that host western military facilities, saying the U.S. missile shield plans threaten Russian security.

That would be the Kremlin’s first new European base since the end of the Warsaw Pact, and could seem a response to NATO’s expansion in the region.