Russia-US tensions mount as Lavrov escalates argument with Rubio Russian Foreign Minister Sergei Lavrov on Friday called for “clarification” of the US role in trying to end the war in Ukraine, in a letter to his counterpart Marco Rubio. Tension between Russia and the US over Washington's efforts to end the Ukraine war has grown since the US and Israel launched their war on Iran in February. Russia has welcomed efforts to end the war on Iran and has provided some military and intelligence assistance to Tehran.