LONDON, June 20 (Reuters) - Russia warned NATO member Lithuania on Monday that unless the transit of goods to Russia's Kaliningrad exclave on the Baltic Sea was swiftly restored then Moscow would take undisclosed measures to defend its national interests.With east-west relations at a half-century low over Russia's Feb. 24 invasion of Ukraine, Vilnius banned the transit of goods sanctioned by the European Union through Lithuanian territory to and from the exclave, citing EU sanction rules.Russia's foreign ministry summoned Lithuania's top envoy in Moscow to deliver a protest while the Kremlin said the situation was beyond serious."The situation is more...