US Vice President Joe Biden called Russian Prime Minister Dmitry Medvedev on Monday, and called on Moscow to pull back forces in Crimea, the White House said.
Officials noted that the call took place after Medevedev spoke over the weekend to Ukraine's new prime minister Arseniy Yatsenyuk, but did not give further details.
"The vice president urged Russia to pull back its forces, support the immediate deployment of international monitors to Ukraine, and begin a meaningful political dialogue with the Ukrainian government," a White House statement said.
Biden held repeated conversations with ousted Ukranian president Viktor Yanukovych throughout Ukraine's political crisis and has continued his role as a US conduit to Ukraine's interim government.
Monday's call came as Washington mulled its options on how to respond to Moscow's incursion into Ukraine and after a tense 90-minute telephone call between President Barack Obama and Russian President Vladimir Putin on Saturday.