US Vice-President Joe Biden has said the US stands with Ukraine’s new leaders against “humiliating threats” – an apparent reference to Russia.
He was speaking during a meeting in parliament in Kiev, as part of a show of support for Kiev’s new pro-Western government.
He also had talks with acting President Olexander Turchynov and interim Prime Minister Arseniy Yatsenyuk.
Meanwhile, funerals were due to take place for three men shot on Sunday.
The men were killed during a raid on a checkpoint manned by pro-Russian separatists near the town of Sloviansk in eastern Ukraine.
The circumstances remain unclear. The local separatists said the attack was carried out by ultra-nationalist Right Sector militants. Kiev called it a “provocation” staged by Russian special forces.
Mr Biden said Ukraine also faced “very daunting problems” and stressed the need for the new authorities to tackle corruption, which he described as “endemic in your system”.
He told members of parliament: “The opportunity to generate a united Ukraine, getting it right is within your grasp.”
Russian Foreign Minister Sergei Lavrov accused the Kiev authorities on Monday of breaking last week’s Geneva accord on resolving the Ukraine crisis.
Pro-Russian militants are still holding official buildings in at least nine towns and cities in the Donetsk region
Flowers lie on the road near the site of Sunday’s fatal shooting on the edge of Sloviansk
He said the Kiev government – not recognised by Moscow – had not moved to disarm illegal groups, especially Right Sector.
The authorities in Kiev say they were surprised by Mr Lavrov’s remarks and blame Russia for the instability.
A phone conversation between the US secretary of state and Russia’s foreign minister earlier led to both sides blaming the other over the crisis.
In a phone call, Mr Lavrov urged US Secretary of State John Kerry “to influence Kiev, to prevent hotheads there from provoking a bloody conflict,” according to the Kremlin.
Meanwhile, the US state department said Mr Kerry “urged Russia to take concrete steps to help implement the Geneva agreement, including publicly calling on separatists to vacate illegal buildings and checkpoints”.
Correspondents say the US has drawn up plans for further economic sanctions should Russia fail to make good on its Geneva commitments, our correspondent adds.
Russian Prime Minister Dmitry Medvedev told the Russian parliament on Tuesday that Russia would be able to “minimise the consequences” of any further sanctions. BBC