Two warships Russia is buying from France will be difficult to operate and maintain because of a lack of proper fuel and possible other problems, a top official said on Tuesday.

"The problems Russia may face when operating the Mistrals are currently under consideration," Russian news agencies quoted deputy prime minister in charge of defence issues, Dmitry Rogozin, as saying.

Russia and France in 2011 signed the contract worth over a billion euros for Moscow to buy the two ships, its first ever purchase of military hardware from a NATO member.

Rogozin, Russia's former NATO envoy, said the type of fuel needed for the helicopter-carrier warships was not produced in the country so Russian chemists would have to find a solution.

The state ITAR-Tass news agency quoted a military expert as saying that Mistral-class warships needed around 50 types of fuel many of which were not produced in Russia.

The country also did not have special tankers needed to refuel the warships at sea, the expert, who the news agency said did not want to be named, was quoted as saying.

"Even in time of peace operating the Mistrals will most likely become a true torture for our seamen to say nothing of a period of threat and especially real military engagement," ITAR-Tass quoted the expert as saying.

Last month, Rogozin was quoted as saying that Mistral-class ships do not operate properly under temperatures of seven degrees below zero, making them unusable in the waters of the Russian Arctic.

Negotiations over the purchase began in 2009 but repeatedly stalled over price and technology transfer amid strong resistance from the powerful military lobby in Russia.

Under the deal, two more Mistral ships are to be built in Russia to the French design in an unprecedented transfer of technology.

In an apparent bid to calm the storm caused by the remarks, Rogozin wrote on his blog that Russia was fulfilling its obligations on the first two ships and any "questions that have unexpectedly appeared" would be discussed in talks this month.

Over recent months Medvedev, now prime minister, has repeatedly come under criticism for a number of decisions while he served as president in what analysts describe as a campaign to discredit him.

In November, President Vladimir Putin fired defence minister Anatoly Serdyukov over a corruption scandal. The minister had spearheaded a major military reform which included the Mistral purchase.