Tens of thousands have joined a rally in the Russian capital Moscow to oppose its intervention in Ukraine, a day before Crimeans vote on whether to secede and join Russia.
Holding Russian and Ukrainian flags, they shouted: "The occupation of Crimea is Russia's disgrace." A smaller pro-Moscow rally was being held elsewhere.
Moscow supports the vote, which Ukraine and the West have dismissed as illegal.
Kiev says Russian "provocateurs" are behind clashes in eastern Ukraine.
Three people have died in pro- and anti-Moscow rallies in the cities of Donetsk and Kharkiv with sides blaming each other.
Russia's military intervention in the Crimean peninsula - part of Russia until 1954 and host to its Black Sea fleet - followed the fall of Ukraine's pro-Moscow President Viktor Yanukovych on 22 February.
Mr Yanukovych's decision in November not to sign a deal on closer ties with the European Union - opting instead for closer ties with Russia - had sparked months of protests.
Both the US and EU have threatened sanctions against Moscow.
On Saturday, the UN Security Council failed to adopt a US-drafted resolution that defines Crimea's referendum as illegal.
Thirteen members backed the resolution and China abstained, but Russia vetoed its passage.
After two people were killed in Kharkiv on Friday, interim Ukrainian Prime Minister Arseniy Yatsenyuk said on his Facebook page: "Hired provocateurs from a neighbouring state are already playing on this situation and preparing provocations professionally.
"Former Ukrainian leaders, charged with crimes, are funding the planned disturbances in the country's south-east in co-ordination with the Russian extremist forces. Don't let them manipulate you."
Interim President Oleksander Turchinov echoed the charge, saying "Kremlin agents" were organising and funding the protests in eastern Ukraine.
Moscow denies this, vowing to protect its "compatriots" from far-right radicals.
Russia's foreign ministry said in a statement on Saturday that it was "receiving many requests to protect peaceful citizens" in Ukraine.
The ministry said it would consider the requests.
In other developments:
- Ukraine says it has repelled an attempt by Russian troops to move from Crimea into a neighbouring region of Ukraine
- US Vice-President Joe Biden will travel to Poland and Lithuania early next week to discuss ways to support Ukraine's sovereignty, as well as Nato members' reciprocal defence commitments
- The Pentagon says it will keep its aircraft carrier battle group in the Mediterranean Sea for several days longer than planned because of the Ukraine crisis
- In the eastern Ukrainian city of Donetsk, hundreds of pro-Moscow protesters smashed the windows of the local offices of the security service and demanded the release of their detained leader Pavel Gubarev
Sense of shame
Tens of thousands - possibly as many as 50,000 - attended the rally in Moscow to oppose the government's intervention in Crimea and eastern Ukraine.
"Hands off Ukraine," some of the protesters shouted.
"People who want peace between Ukraine and Russia have gathered here. That's why I'm here," one of the participants said.
There is a sense of shame among protesters over the course that Moscow is following, says the BBC's Richard Galpin, at the rally.
One man told the BBC he felt Russia was turning back to the days of Soviet dictator Joseph Stalin.
At the pro-Kremlin rally, about 15,000 supporters of President Vladimir Putin came out to support the Crimean referendum.
Many of the protesters wore identical red outfits and carrying Russian and Soviet flags
"We are for friendship of the Russian and Ukrainian peoples. We want to say a firm 'No' to the fascist junta that came to power in Ukraine and therefore we naturally want to support our comrades in Ukraine," one man said.
On Friday, US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov held six hours of talks in London, but failed to reach agreement on how to resolve the Ukraine crisis.
Mr Lavrov stressed that Moscow would "respect the will of the people of Crimea".
Mr Kerry said the US acknowledged Russia's "legitimate interests" in Ukraine and had told Mr Lavrov that there would be consequences if Russia "does not find a way to change course".
Are you in Crimea? Are you planning to vote in the referendum? Email us at email@example.com with the subject heading 'Crimea vote'.