Ukrainian special forces moved against pro-Russian demonstrators occupying a government building in the eastern city of Donetsk late Monday, CNN reported.
The troops cleared armed protesters from the headquarters of Ukrainian security services in the city, one of three where pro-Moscow uprisings took place over the weekend, acting President Oleksandr Turchynov's office announced Monday night.
The report came several hours after Turchynov blamed "separatist groups coordinated by Russian special services" for the revolts, which he said echoed events leading to the Russian annexation of Crimea three weeks ago.
"Enemies of Ukraine are trying to play out the Crimean scenario, but we will not let this happen," Turchynov said in a televised message, according to CNN.
Pro-Moscow protesters seized government buildings, raised Russian flags and declared new governments in the cities of Donetsk, Luhansk and Kharkov on Sunday.
Ukrainian Prime Minister Arseniy Yatsenyuk said the goal of the protesters is "to destabilize" the country, allowing "foreign troops to cross the border and seize the territory of the country."
"We will not allow it," Yatsenyuk declared.
Russia, which has an estimated tens of thousands of troops near the Ukrainian border, said it was "watching closely" and told Ukraine to quit blaming it for Ukrainian problems. President Vladimir Putin's government pushed Ukraine to set up a federal system in which regions with ethnic Russian majorities would have more autonomy, and its foreign ministry urged Ukraine to enter into talks over the issue.
"Ukrainian people want to get a clear answer from Kiev to all their questions. It's time to listen to these legal claims," a Foreign Ministry statement quoted by CNN read. The Ukrainian government was acting "irresponsibly," it said.
Donetsk has been the seat of pro-Russian tensions since earlier this month, when neighboring Crimea held a controversial referendum vote and was annexed by Moscow after a de facto military invasion of the region.
In Washington, U.S. officials urged Russian President Vladimir Putin's government to disavow the protests and warned further Russian intervention in Ukraine would bring stiffer economic sanctions than those already imposed over the Crimean annexation.
"If Russia moves into eastern Ukraine, either overtly or covertly, this would be a very serious escalation," White House spokesman Jay Carney told reporters.
"We call on President Putin and his government to cease all efforts to destabilize Ukraine. And we caution against further military intervention," he added.