Russia on Saturday expressed hopes for the success of the OSCE monitoring mission in Ukraine, while stressing the observers were excluded from Crimea after its takeover by Moscow.
Former US secretary of state Hillary Clinton on Tuesday accused Russian President Vladimir Putin of attempting to "rewrite the boundaries" of post-World War II Europe.
German Chancellor Angela Merkel and US President Barack Obama in a phone call condemned Russia's moves to annex Crimea but said "a clear path" remains to solve the crisis diplomatically.
Crimea provides itself with gas fully; if Kiev should try to disrupt electricity supply, that would be regarded as sabotage Crimea's Head of Government said.
Beyond Sunday's referendum on whether Crimea should join Russia, one big question looms: how viable will the disputed peninsula be if it decides to split from Ukraine?
Ukraine's acting president has said the country will not use its army to stop Crimea from seceding, the latest sign that a Russian annexation of the strategic peninsula may be imminent.
Experts warn that any resolutions from UN are unlikely: When big powers in the Security Council are at loggerheads, the UN has always proved to be politically impotent.
Diplomatic efforts to calm the Ukraine crisis inched forward Monday, with Moscow saying it would consider Western proposals for talks on the standoff but insisting Crimea had the right to secede.
Rallies were planned across Ukraine on Sunday as the troubled ex-Soviet state struggled to contain upheaval amid a standoff between Russia and the West over Crimea that shows no sign of easing.
The number of Ukrainian servicemen who had taken an oath of loyalty to people of Crimea doubled over the past 24 hours to exceed 3,000, a source in the government of Ukraine's autonomous republic told Itar-Tass on Monday.