U.S. Vice-President Joe Biden is to meet Ukraine's new leaders in a show of support for the pro-Western government, BBC News reported.
Biden is due to discuss the upcoming elections with the country's interim prime minister and president during his visit to Kyiv. A phone conversation between the U.S. secretary of state and Russia's foreign minister earlier led to both sides blaming the other over the crisis.
Meanwhile, funerals are due to take place for three men shot on Sunday, April 20.
The men were killed during a raid on a checkpoint manned by pro-Russian activists near the town of Sloviansk in eastern Ukraine.
The circumstances remain unclear. The local activists said the attack was carried out by ultra-nationalist Right Sector militants. Kyiv called it a "provocation" staged by Russian special forces.
Russian Foreign Minister Sergei Lavrov accused the Kyiv authorities on Monday of breaking last week's Geneva accord on resolving the Ukraine crisis. He said the Kyiv government - not recognised by Moscow - had not moved to disarm illegal groups, especially the Right Sector.
The authorities in Kyiv say they were surprised by Lavrov's remarks and blame Russia for the instability.
In a phone call, Lavrov urged U.S. Secretary of State John Kerry "to influence Kyiv, to prevent hotheads there from provoking a bloody conflict," according to the Kremlin.
Meanwhile, the U.S. state department said Kerry "urged Russia to take concrete steps to help implement the Geneva agreement, including publicly calling on separatists to vacate illegal buildings and checkpoints".
Judging by the contrasting accounts of its contents, the conversation simply led to both sides blaming the other for the fact that very little has changed in Ukraine since agreement was reached last Thursday, says the BBC's David Willis in Washington.
The U.S. has drawn up plans for further economic sanctions should Russia fail to make good on its Geneva commitments, our correspondent adds.