U.S. Secretary of State John Kerry has told his Russian counterpart Sergei Lavrov that Russia must pull back its troops from the Ukrainian border to deescalate the tension following Crimea’s takeover by Moscow.

Victoria Nuland, U.S. Assistant Secretary of State for European and Eurasian Affairs, will visit Bulgaria on Monday. The talks were scheduled between Nuland and government representatives from Bulgaria, where bilateral cooperation

U.S. Secretary of State John Kerry began one-on-one discussions Sunday night with Russian Foreign Minister Sergei Lavrov, in an effort to find a solution to the crisis in Ukraine, which has ratcheted up tensions between Moscow