France is suspending the planned delivery of a warship to Russia, citing the "current situation" in eastern Ukraine.
The office of French president Francois Hollande announced the suspension following growing speculation about the contract, which is the biggest arms sale ever by a Nato country to Russia.
The Vladivostok, the first of two Mistral-class helicopter carriers ordered by Russia, was due to be delivered as part of the 1.2 billion euro (£950 million) contract.
France has come under intense pressure from allies to suspend the sale because of tensions between Russia and Ukraine.
The first of the two ships, the Vladivostok, is docked at the French port city of Saint Nazaire, where about 400 Russian sailors have spent months training aboard the vessel.
The second ship, named the Sevastopol, after a port in the Russia-annexed Crimean Peninsula, was slated for delivery next year and recently arrived at the Saint Nazaire docks for finishing touches.
Today's statement, like a previous suspension of the delivery, stopped short of cancelling the deal, suggesting the French government is reluctant give up on a contract worth more than a billion euros as well as thousands of jobs at a time of an economic slump in France.
The Vladivostok can carry 700 troops, 16 helicopter gunships and up to 50 armoured vehicles.
Analysts have said the warships would give Russia an enhanced ability to move large numbers of troops and equipment, but were not game-changers for Moscow's military.
Russia's deputy defence minister Yury Brosiov told the RIA Novosti news agency that Moscow was not planning to take any immediate action against France for delaying the deal.
He said: "We are satisfied, it is the French who are not satisfied, and we are going to patiently wait.
"Everything is spelled out in the contract, and we are going to act in accord to the contract like all civilised people."