Ukraine faced a fresh secessionist crisis on Monday as pro-Kremlin militants occupying the Donetsk government seat proclaimed independence from Kiev and vowed to hold a referendum on joining Russia.
Pro-Russian activists who seized the main administration building in the eastern Ukrainian city of Donetsk deploy a flag of the so-called Donetsk Republic and hold a Russian flag on April 7, 2014, in Donetsk
The declaration and accompanying appeal for Russian military assistance put the culturally splintered nation of 46 million in danger of disintegration and intensified pressure on Western powers to act.
The White House responded by calling on the Kremlin to stop trying to "destabilise Ukraine" -- a comment that echoed Kiev's earlier charge of Russia seeking to "dismember" its neighbour.
But Moscow brushed off the accusations and called the latest unrest a sign of Kiev's Western-backed leaders' ineptitude and illegitimacy.
The Cold War-style war of words over the ex-Soviet nation's future comes with the added urgency of the Ukrainian border being watched by Russian soldiers who had already annexed Crimea in response to last month's ouster in Kiev of a Moscow-backed regime.
Several heavily Russified eastern regions have recently been hit by calls for referendums on joining Russia when Ukraine holds snap presidential polls on May 25.
The political pressure on Kiev's embattled leaders reached boiling point on Sunday when thousands of activists chanting "Russia!" seized administration buildings in Kharkiv and Donetsk as well as the security service headquarters in the eastern region of Lugansk.
The Donetsk activists went one step further on Monday by proclaiming the creation of a sovereign "people's republic" in the region of about five million people.
A video posted on YouTube showed one bearded Russian speaker telling the packed assembly from a podium: "Seeking to create a popular, legitimate, sovereign state, I proclaim the creation of the sovereign state of the People's Republic of Donetsk."
More footage aired on Ukraine's Channel 5 television showed an unidentified speaker asking Russian President Vladimir Putin to send a "peacekeeping contingent of the Russian army" to Donetsk to help the region stand up to Kiev's rule.
Ukraine's acting President Oleksandr Turchynov accused Russian "special services" of being behind the uprising and ordered extra security personnel to the restless region.
"These actions are meant to destabilise the country, overthrow the Ukrainian government, torpedo the elections and tear our country to pieces," Turchynov said in a nationally televised address.
The Russian foreign ministry responded with a toughly worded statement telling Kiev to "stop pointing the finger at Russia, blaming it for all the problems in today's Ukraine."
But the White House put the onus back on Moscow by describing the latest developments "as the result of increasing Russian pressure on Ukraine."
"We call on President Putin and his government to cease efforts to destabilise Ukraine," White House spokesman Jay Carney said.
Washington's concern underscores the trouble Kiev may have in bringing order to Ukraine's eastern industrial heartland -- a region with ancient cultural and trade ties to Russia.
The Donetsk administration building on Monday remained surrounded by about 2,000 Russian supporters -- some of them armed.
Militants on Monday also seized the Donetsk security service headquarters while rival rallies gripped the heart of the nearby eastern city of Kharkiv that saw its own administration building occupied briefly overnight.
- Seeking to 'dismember Ukraine' -
Much of the blame in Kiev on Monday was being levelled directly at Putin -- a sign of how relations between the two neighbours have plunged in the past few months.
Ukrainian Prime Minister Arseniy Yatsenyuk said Russia was helping orchestrate the occupations in order to find an excuse for a full-out invasion that would punish Kiev for its decision to seek a political and economic alliance with the West.
"This scenario is written by the Russian Federation and its only purpose is to dismember Ukraine," Yatsenyuk told a government meeting in Kiev.
Moscow is now lobbying for Ukraine to be transformed into a federation that allows eastern regions to adopt Russian as a second state language and overrule some decisions coming from Kiev.
The Kremlin has argued the changes were needed because ethnic Russians had allegedly been coming under increasing attack from ultranationalist forces that helped the new leaders ride a wave of anti-government protests to power.
But Washington and its EU allies fear Russia is using the federation idea as an excuse to further splinter Ukraine by granting the Kremlin veto powers over Kiev's regional policies.
The new Kiev government approved a draft reform plan last week that would grant more powers to the regions in line with Western wishes but stopped well short of creating the federation sought by Russia.
And Yatsenyuk on Monday called federalisation a dangerous idea aimed at ruining Ukraine.
"Any call toward federalisation is an attempt to destroy the Ukrainian state," he said.