U.S. Vice President Joe Biden told Russia on Tuesday that "time is short" for action on defusing the crisis in eastern Ukraine, but Moscow said it could handle any tougher economic sanctions the West might impose.
Speaking on a visit to Kiev, Biden called on Moscow to pull back troops built up on Ukraine's borders and to "stop talking and start acting" on getting Russian separatists who have seized control in eastern towns and cities to disarm.
The United States has repeatedly warned Russia it faces "mounting costs" if it fails to ensure full implementation of an international agreement struck last week on calming the crisis. This stipulates the rebels must leave the government buildings that they have occupied in the past two weeks.
Russia has in turn accused the Ukrainian government of stirring up the trouble and told Washington it must influence Kiev to prevent "hotheads" from provoking a bloody conflict.
Biden, however, put the onus on Moscow. "We've heard a lot from Russian officials in the past few days. But now it's time for Russia to stop talking and start acting," he told a news conference. "We will not allow this to become an open ended process. Time is short in which to make progress."
Russia's annexation of Crimea from Ukraine and the eastern rebellion have deepened the worst East-West crisis since the Cold War, and Biden demanded the removal of Russian forces near Ukraine's frontier which Moscow insists are merely on exercises.
"No nation should threaten its neighbours by amassing troops along the border. We call on Russia to pull these forces," Biden said after meeting Ukrainian Prime Minister Arseny Yatseniuk.
Moscow denies it is orchestrating the militants, who say they want the chance to join Crimea in becoming part of Russia following the overthrow of Moscow-backed president Viktor Yanukovich after months of street protests in Kiev.
But Washington, which signed last week's accord in Geneva along with Moscow, Kiev and the European Union, has said it would decide "in days" on additional sanctions if Russia does not take steps to implement the agreement.
In Moscow, Prime Minister Dmitry Medvedev said the country could deal with tougher measures if necessary.
"We shan't give up on cooperation with foreign companies, including from Western countries, but we will be ready for unfriendly steps," he told parliament.
"I am sure we can minimise their impact," he said. "We will not allow our citizens to become hostages of political games."