President Vladimir Putin has rebuffed a warning from US President Barack Obama over Moscow's military intervention in Crimea, saying Russia could not ignore calls for help from Russian speakers in Ukraine.
After an hour-long telephone call, Mr Putin said in a statement on Friday that Moscow and Washington were still far apart on the situation in the former Soviet republic.
Mr Putin said the new authorities there had taken illegitimate decisions on the eastern, south-eastern and Crimea regions and that Russia was acting in full compliance with international law.
The most serious east-west confrontation since the end of the Cold War escalated on Thursday when Crimea's parliament, dominated by ethnic Russians, voted to join Russia. The region's government set a referendum for 16 March, Reuters reports.
European Union leaders and Mr Obama denounced the proposed referendum as illegitimate, saying it would violate Ukraine's constitution.
Before calling Mr Putin, he announced the first sanctions against Russia since the start of the crisis, ordering visa bans and asset freezes against so far unidentified persons deemed responsible for threatening Ukraine's sovereignty.
The EU, Russia's biggest economic partner and energy customer, adopted a three-stage plan to try to force a negotiated solution but stopped short of immediate sanctions. Brussels and Washington also rushed to strengthen the new authorities in economically shattered Ukraine, announcing both political and financial assistance.
In their telephone call, Mr Obama said he urged Mr Putin to accept the terms of a potential diplomatic solution, and said the dispute over Crimea could be resolved in a way that took account of Russia's legitimate interests in the region.
Mr Putin was defiant on Ukraine, where he said pro-Russian President Viktor Yanukovich had been overthrown in an "anti-constitutional coup" in February. However, he stressed what he called "the paramount important of Russian-American relations to ensure stability and security in the world", the Kremlin said.
"These relations should not be sacrificed for individual differences, albeit very important ones, over international problems," Mr Putin said.
He maintained that Moscow was not behind the seizure of Crimea, home of Russia's Black Sea Fleet. Russia says the troops without national insignia that have surround Ukrainian bases are "local self-defence units". The West has ridiculed this argument.
After talks in Rome on Thursday, US Secretary of State John Kerry said Russian Foreign Minister Sergei Lavrov was personally delivering proposals to Mr Putin to end the crisis. Mr Kerry said the executive order signed by Mr Obama on Thursday provided a legal framework for imposing sanctions, but also left open the door for dialogue.
The 28-nation EU welcomed Ukrainian Prime Minister Arseny Yatseniuk to its emergency summit, even though Kiev is neither a member nor a recognised candidate to join the bloc, and agreed to bring forward the signing of the political parts of an agreement on closer ties before Ukraine's elections on 25 May.
"No one will give up Crimea to anyone," Mr Yatseniuk told a news conference in Brussels, while Ukraine's acting president, Oleksander Turchinov, called the planned referendum "a farce, a fake, a crime".
In Crimea, the situation was calm although 35 unarmed military observers dispatched by the pan-European Organisation for Security and Cooperation in Europe were denied entry into the peninsula after landing in the southern Ukrainian port of Odessa.
A UN special envoy who travelled to the regional capital Simferopol on Tuesday was surrounded by pro-Russian protesters, some of them armed, and forced to leave on Tuesday. The United Nations said it was sending its assistant secretary-general for human rights to the region soon.
Paralympic Games boycott
The crisis in Ukraine has prompted a widespread boycott of the Winter Paralympic Games in Russia by politicians and dignitaries from other countries.
The US has withdrawn its delegation to Sochi and many European governments will also stay away, the BBC reports.
Ukraine's Paralympic team members have raised their country's flag without knowing whether or not they will boycott the Games, which were opened by Vladimir Putin on Friday.