The White House said Ukraine's government has the "responsibility to provide law and order" as its troops move against pro-Russia separatists in the country's eastern region.
"These provocations in eastern Ukraine are creating a situation in which the government has to respond," White House spokesman Jay Carney said at a briefing.
The US is "seriously considering" new sanctions against Russia, but is not considering providing lethal aid to Ukraine, he added.
Tensions remain high in eastern Ukraine after at least three died in a day of shooting during what was supposed to be an Easter truce.
In an exclusive interview with NBC News, the Ukrainian Prime Minister warns of the dangers of unchecked Russian expansion and aggression.
Russia, the US and the EU say that all sides have agreed to steps to "de-escalate" the crisis in Ukraine at talks in Geneva.