Ukraine's interim prime minister said on Thursday his country was entering its "most dangerous 10 days" since independence in 1991 and was struggling to counter pro-Russian separatists on the verge of taking over the industrialized eastern heartland.
Arseniy Yatseniuk, in an interview with the Financial Times, accused Moscow of plotting to foment more clashes during the May Day holidays when nostalgia for Soviet victories and achievements tends to peak.
Pro-Russians strengthened their grip on the east of Ukraine on Thursday, storming the regional prosecutor's office in the town of Donetsk driving the police out and ransacking the building. The Kiev authorities fear the secessionists will put on a bigger show of strength on May 9, the commemoration of the Soviet Union's victory over Nazi Germany.
On May 11, pro-Russian separatists who have seized government buildings in about a dozen cities in the Donetsk and Lugansk regions, plan to hold a referendum on independence and later unification with Russia.
"They will play on this Soviet-style legacy and try to provoke and artificially make clashes," Mr Yatseniuk said. "They … usually have 10 to 20 well-trained Russian agents who storm the buildings, then grab indigenous protesters, disappear and move to another city."
German chancellor Angela Merkel telephoned Vladimir Putin, the Russian president, in the latest western attempt to dissuade Moscow from stoking the crisis. Ms Merkel will hold talks on the Ukrainian crisis with President Barack Obama in Washington on Friday.