Russian armed forces are said to have taken weapons from a radar base and naval training facility in Ukraine’s Crimea region, according to Russian news agency Interfax.
The Ukrainian government has now called up all military reservists.
Russian servicemen apparently urged Ukrainian forces to side with Crimea’s “legitimate” leaders.
The alleged move follows Saturday’s vote in the State Duma to deploy troops in Ukraine.
As tension builds between the two countries, the governor of Russia’s Bolgograd region announced armed groups had tried to block a road running from Moscow into the Crimea region.
On Sunday morning a small, pro-Russian rally took place in Simferopol, while unidentified armed men were once more seen patrolling outside the nearby Governing Council Offices.
Meanwhile, in Kyiv, some are demanding more international support.
British Foreign Secretary, William Hague has released a statement saying:
“We will be using every possible diplomatic channel to make clear our concern and to seek clarification from Russia of its intentions and to ask for a de-escalation by all concerned.”
Get a different perspective
Every story can be told in many ways: see the perspectives from Euronews journalists in our other language teams.