Ukraine's Prime Minister Arseniy Yatsenyuk has pledged "special status" for the Russian language and a broad decentralisation of power in a bid to defuse pro-Moscow protests sweeping the east of the country.
In a joint TV address on Friday, Yatsenyuk and acting President Oleksander Turchinov called for national unity, urged people to refrain from violence and said they would support constitutional change, decentralising more power to local councils, including over their official language - a key demand of Russian-speakers.
"We will accord special status to the Russian language and guarantee to protect it," Yatsenyuk said, adding that "major" constitutional reforms would also see a raft of powers handed to the regions.
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Russia, meanwhile, said it was disappointed with the United States' assessment of an international deal, reached in geneva on Thursday, to defuse the crisis in Ukraine, saying the threat of new sanctions against Moscow by Washington was "completely unacceptable."
The Foreign Ministry accused in a statement US officials of seeking to "whitewash" what it said was the use of force by Kiev's authorities against protesters in Ukraine's Russian-speaking eastern provinces.
A surprising deal reached by the US, EU and Russia on Thursday calls for disarming all paramilitary groups and the immediate return of all government buildings seized across the country.
The White House warned Russia on Friday that Moscow would face tougher sanctions if it failed to abide by the new international deal or moved to send Russian forces into eastern Ukraine.
"Those costs and sanctions could include targeting very significant sectors of the Russian economy," Susan Rice,
President Barack Obama's national security adviser, told reporters.
The pro-Russian groups in question, however, are resisting any attempts to disarm or remove them from occupied buildings until pro-Ukraine groups are removed from buildings and the government in Kiev resigns.
Denis Pushilin of the self-appointed Donetsk People's Republic told reporters the occupiers do not recognise the Ukrainian government as legitimate.
"This is a reasonable agreement but everyone should vacate the buildings and that includes (Arseniy) Yatsenyuk and (Oleksandr) Turchynov," he said.
Ukraine has scheduled a presidential election for May 25, but Pushilin reiterated a call to hold a referendum on self-determination for the Donetsk region by May 11.
Such a referendum in Crimea led to its annexation by Russia.
Russian Foreign Minister Sergey Lavrov on Thursday emphasised that the requirement to abandon occupied building applied to all parties, an apparent reference to the ultranationalist Right Sector, whose activists are occupying Kiev city hall and a Kiev cultural centre.