Russian President Vladimir Putin says there is no need yet to send Russian troops into Ukraine.
But Russia reserves the right to use “all means” to protect citizens in the east of the country, Mr Putin said.
He denied Russian troops had besieged Ukrainians based in Crimea – they were pro-Russian “self-defence” forces.
Mr Putin called the toppling of President Viktor Yanukovych in the capital Kiev an “anti-constitutional coup and armed seizure of power”.
Crimea remains a major focus of the crisis, as troops in what appear to be Russian uniforms surround Ukrainian military bases and other installations. Russia is de facto in control of the peninsula.
Tensions were especially high at Belbek airbase near Sevastopol, the port city which is the base of Russia’s Black Sea Fleet. Pro-Russian forces fired warning shots in the air, and Ukrainian troops later marched away from the base.
Meanwhile, two Ukrainian warships are reported to be blocked by a Russian ship in the port of Sevastopol.
There is intense diplomatic activity aimed at defusing the crisis.
US Secretary of State John Kerry has arrived in Kiev to meet Ukraine’s new leaders and show support for the country’s sovereignty.
He will head to Kiev’s Independence Square – the Maidan – to lay flowers for victims of last month’s violence, before heading into meetings with the new government.
Russian Foreign Minister Sergei Lavrov is expected to meet the EU foreign policy chief, Catherine Ashton, in the Spanish capital Madrid.