The referendums are due to take place on Sunday and millions of ballot papers have been prepared.
President Vladimir Putin said Russia pulled back its troops from the Ukrainian border and called on separatists in the country\’s south and east to postpone planned 11 May plebiscites over regional autonomy.
The move was announced after a Kremlin meeting with the current Organisation for Security and Cooperation in Europe chief, Didier Burkhalter, on Wednesday.
"We ask the representatives of the southeast to postpone the referendums planned for May 11 in order to create the conditions necessary for dialogue," Putin said after the meeting.
Pro-Russian activists said they would discuss Putin\’s call for postponement at a meeting of their assembly on Thursday.
"Tomorrow we will discuss that at the people\’s assembly," Denis Pushilin, a leader of the self-declared Donetsk People\’s Republic, told Reuters.
"We have the utmost respect for President Putin. If he considers that necessary, we will of course discuss it."
Separatist leaders in Donetsk and Luhansk say they will put the matter before "people\’s councils".
Pro-Russian activists who have seized government buildings in eastern regions, such as Donetsk and Luhansk, had announced plans to stage polls on secession from Kiev following the protest-led ouster in February of a Kremlin-backed regime.
Ukraine\’s Interior Minister says 30 pro-Russian insurgents were killed during Monday\’s military assault to expunge anti-government forces in the eastern town of Slovyansk.
Arsen Avakov said Tuesday that four government troops also died and another 20 were injured during the gun battles.
Separately on Tuesday, authorities suspended flights in and out of eastern Ukraine\’s industrial hub of Donetsk. It is unclear why the flights were suspended or how long the suspensions were to remain in effect.
With violence on the rise in Ukraine, United Nations Secretary-General Ban Ki-moon has told the French News Agency he will offer himself as a mediator before the situation creates huge consequences beyond anybody\’s control.
Ukraine is facing its worst crisis in decades as citizens fight over whether to look toward Europe or improve ties with Russia. Pro-Russian separatists control about a dozen eastern Ukrainian towns and cities, demanding the right to vote on whether to split with Ukraine and join Russia.
A similar referendum in Crimea in March led to the Russian annexation of the Ukrainian peninsula and the current crisis.
Russia\’s Foreign Ministry is calling on Ukraine to withdraw its troops from the east and open talks on ways to resolve the political crisis.
Interim Ukrainian Prime Minister Arseniy Yatsenyuk accuses Russia of seeking to destroy Ukraine by engineering what he says is a "well-planned provocation" against the government.
Russia says the new Ukrainian government is controlled by anti-Russian nationalists and neo-Nazis. It says it has the right to protect Russian speakers.
On Tuesday, British Foreign Minister William Hague, who was also in Vienna for the Council of Europe meeting, accused Russia of trying to prevent or disrupt Ukraine\’s May 25 presidential election.
And French President Francois Hollande warned Tuesday that there will be "chaos and the risk of civil war" if the May 25 vote is not held.
Forty-six people died in the Black Sea city on Friday in a fire at an official building and fighting between pro-Russian and pro-Ukrainian protesters.
The 25 May presidential election was called after pro-Kremlin President Viktor Yanukovych was overthrown by pro-Western protesters in February.
The votes have been denounced as illegal by both Kiev and its allies in Washington and the European Union.