Ukraine has urged its citizens living in Russia to leave the country immediately, BBC reported.
Up to three million Ukrainians are believed to be living in Russia and many have family in both countries.
In addition, a state of emergency is to be declared in Ukraine, lasting 30 days, the country's top security official said.
Ukraine is also conscripting reservists into the regular military as it braces for a possible invasion by its neighbour, Russia.
Western countries and their allies have imposed sanctions on Russian banks and MPs, as the crisis escalates. But critics, among them the UK's Labour Party, say the measures so far are not strong enough.
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It's not clear if any new Russian troops have yet been sent into the two regions, which are run by Moscow-backed separatists.
A state of emergency across the whole country is set to be declared, following a recommendation from Ukraine's security council. This will last 30 days, but is subject to approval by the Ukrainian parliament - expected later on Wednesday, BBC reported.
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Ukraine military has also called up a first wave of reservists - aged 18 to 60 - to join the regular armed forces.
