Ukraine has formally called off the Easter truce against pro-Russian separatists in the east and says anti-terrorist operations are on again, while Russia threatens to retaliate.
First Deputy Prime Minister Vitaliy Yarema told reporters during a Cabinet meeting Wednesday that what he calls "appropriate steps" will be taken and that results will be seen shortly.
Yarema said Ukraine has gotten assurances from the United States that it would not be left alone to face Russian aggression. He expressed hope that the U.S. support will be more substantive.
In Moscow, Russian Foreign Minister Sergei Lavrov told state television that Russia would retaliate if its legitimate interests or the Russian people are attacked. He said Russia's response would be the same as it was in South Ossetia in 2008, which led to a brief war with Georgia.
The Pentagon said Tuesday it is sending 600 U.S. troops to Poland and the Baltics to "send a message" to Moscow and to reassure American allies and partners.
U.S. Vice President Joe Biden ended a two-day visit to Kyiv Tuesday, calling on Moscow to honor its promise to withdraw support for armed pro-Russian separatists in Ukraine.
Ukrainian military moves last week to drive the separatists from government buildings they have seized in about a dozen cities failed.
An agreement signed in Geneva last week aimed at cooling tensions in Ukraine has gone nowhere and the pro-Russians are showing no signs of backing down.
Pro-Russian gunmen are demanding the right to hold referendums on splitting with Ukraine and joining Russia. A vote last month in Crimea led to the Russian annexation of the Ukrainian peninsula.