Ukraine's ousted leader has urged his former citizens to press for a vote to determine the status of their regions, a call echoing Russia's push to turn the country into a loosely knit federation.
Viktor Yanukovych, the former leader who fled to Russia last month after three months of protests, raised the threat of further instability in Ukraine's Russian-speaking eastern provinces where many resent the new Ukrainian government.
Deep divisions between eastern regions, where many favour close ties with Moscow, and the Ukrainian-speaking west, where most want to integrate into Europe, continue to fuel tensions.
The Crimea peninsula, where ethnic Russians are a majority, voted this month to secede from Ukraine before Moscow formally annexed it, a move that Western countries have denounced as illegitimate.
Speaking from Russia, Mr Yanukovych urged Ukrainians to demand a "referendum that would determine the status of each region in Ukraine", in a statement carried by the ITAR-Tass news agency.
Moscow has pushed strongly for federalising Ukraine - giving its regions more autonomy - but Ukraine's interim authorities in Kiev have rejected such a move.
Following the statement, Ukrainian prosecutors opened a new investigation against Mr Yanukovych on charges of calling for the overthrow of the country's constitutional order.
Mr Yanukovych's biggest rival, former prime minister Yulia Tymoshenko, attacked the statement, accusing him of being "a tool aimed at destroying the independence of Ukraine". Ms Tymoshenko is running in Ukraine's next presidential election, scheduled for May 25.
The Ukrainian government and the West have voiced concern about Russian troops' build-up near the border that stoked fears of an invasion. Russia's president Vladimir Putin has warned that he could use "all means" to protect people in Ukraine from radical nationalists.
The Russian Foreign Ministry said in a statement that Moscow allowed observation flights over the border by Ukrainian, US, German and other Western officials. It said if any major troop concentrations had been spotted during the flights, the West would have spoken out.
Russia also kept pushing its long-held contention that ethnic minorities in Ukraine are living in fear after the removal of Mr Yanukovych and the coming to power of interim authorities. The Foreign Ministry statement said not just ethnic Russians, but Germans, Hungarians and Czechs in Ukraine also feel in peril.
"They are unsettled by the unstable political situation in the country and are seriously afraid for their lives," the statement said without citing specific incidents.
There have been no reported threats toward ethnic minorities in Ukraine.
Russia also said it had responded to Western sanctions over Ukraine but made no new names public.
Foreign minister Alexander Lukashevich said some Western nations have followed the US example and expanded their sanctions against Russia, adding that Moscow had taken "retaliatory measures, which are largely tit-for-tat".
He would not elaborate on who the new targets were.
The US, the European Union and Canada have slapped Russia with travel bans and asset freezes targeting its officials and lawmakers over the annexation of Crimea. US and Canadian sanctions included businessmen close to Mr Putin and a Russian bank, while the EU, which has much stronger economic ties with Russia, has limited its sanctions to officials and politicians.
Russia has responded by slapping travel bans on nine US and 13 Canadian officials and lawmakers, but so far has not retaliated against the EU.