President Barack Obama and German Chancellor Angela Merkel say the presence of Russian soldiers in Ukraine, the buildup of Russian troops along the Ukrainian border and Russian shelling into Ukraine represent dangerous escalations of tensions by Moscow.
The White House says the two leaders agree that a Russian convoy that entered Ukraine without approval is yet another provocation by Moscow that violates Ukraine's sovereignty.
Obama and Merkel spoke Friday while Obama vacationed in the island resort of Martha's Vineyard.
Russia says the convoy that entered Ukraine on Friday is for humanitarian purposes, but Ukraine and the U.S. say the Russians failed to abide by conditions set by Ukraine and the International Red Cross.
Obama and Merkel agree that Russia must remove the convoy and withdraw from Ukrainian territory.