United States Secretary of State Marco Rubio told his Russian counterpart Sergei Lavrov that the United States is committed to working to end the war in Ukraine, the State Department said Monday."The United States is serious about facilitating an end to this senseless war," State Department spokeswoman Tammy Bruce said in a readout of Sunday's call, which was already announced by Russia.She said Rubio spoke to Lavrov about "the next steps in Russia-Ukraine peace talks and the need to end the war now."The call took place before President Vladimir Putin on Monday offered a three-day truce to coincide with Moscow's commemorations for the end of World War II.Rubio said Sunday that this week will be crucial in assessing efforts to end the war, which United States President Donald Trump has promised to stop on the first day of his presidency.In the interview Sunday with NBC News' Meet the Press, Rubio said that there were "reasons to be optimistic, but there are reasons to be realistic as well," and that the United States could decide to focus on other priorities.