Russia has stationed about 4,000 troops with their equipment and ammunition in north Crimea on the border with Ukraine.
"According to our information, almost all military units of the Russian Federation stationed in the north of Crimea were pushed to the administrative border with Ukraine, Press TV reported Saturday citing the spokesperson of Ukraine's National Security and Defense Council, Andriy Lysenko.
The move comes as Russian President Vladimir Putin said he has approved the establishment of a Russian military task force in Crimea.
Moscow has also accepted a peace agreement with Kiev in a bid to end five months of conflict in the eastern regions of Ukraine.
The new development also came after pro-Russia forces in Ukraine's eastern regions recently rejected a law passed by Kiev that grants limited self-rule to the war-torn areas.
Under the law, Ukraine's eastern regions of Donetsk and Lugansk will be offered three-year limited self-rule.
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Pro-Russia militias in the region have been fighting for independence for the past five months.
Earlier this year in March, Crimea's largely Russian-speaking residents voted in a referendum to break away from Ukraine and join Russia.
The Ukrainian government, US and EU rejected the referendum and condemned the joining of Crimea to Russia.
However, President Putin signed into law the documents officially making Crimea part of Russian territory. Putin said the move was made based on international law.
Located on the northern coast of the Black Sea, the Crimea Peninsula is of high strategic value. It is also of importance economically as the peninsula is home to several natural gas fields onshore and offshore, which are connected to Ukraine's pipeline system.