Russia has demanded an official explanation from France over its failure to deliver a Mistral-class warship due to concerns about Moscow's role in Ukraine, a military source said Tuesday.

Moscow has written to France's overseas arms exporter in a move that could pave the way for legal claims against Paris, an unnamed official at Russia's Federal Service for Military-Technical Cooperation told state-run RIA Novosti news agency.

"In order to determine our future decisions -- whether we will go to court or give France more time -- Russia must have a written explanation of the situation," the source said.

France's defence minister warned January 1 that Paris will only deliver two warships ordered by Russia if there is concrete signs of lasting peace in Ukraine.

Paris in November delayed delivery of the first vessel, which was set for autumn 2014, "until further notice."

Russia has been accused by the West of arming and bankrolling a rebellion in eastern Ukraine, a charge Moscow denies.

Sanctions imposed by the European Union and the United States on Russia have complicated France's commitment to the 1.2 billion-euro deal to deliver the two Mistral-class warships -- even though the order was made long before the crisis erupted.