Russia's state arms exporter on Wednesday praised France for sticking by a contract to build two Mistral warships for the Russian navy despite US objections to the project.

Work in the 1.2 billion euro ($1.6 billion) deal for two Mistral-class helicopter carriers is proceeding on schedule, demonstrating "France's reliability as a partner," a spokesman of Rosoboronexport was quoted by ITAR-TASS as saying.

The comments come after Foreign Minister Laurent Fabius on Tuesday defended the sale despite US opposition, but kept the door open to reexamining the contract in October, when the first warship is scheduled to depart the shipyard for deployment in the Russian fleet.

"The rule with contracts is that contracts which have been signed are honoured," he said while on a trip to Washington. "Legally, we don't have the possibility of not honouring them."

Rosoboronexport has stressed that France will be required to pay heavy penalties if the deal is cancelled.

Washington expressed concern at the deal earlier this month after Russia completed the stern section of the second ship that is scheduled to be towed to France in June to be welded with the hull.

The ship will be called The Sevastopol, named after the port city on the Crimean peninsula that Moscow annexed in March.

France agreed in 2011 to sell two Mistral-class helicopter carriers to Russia, attracting criticism from several NATO allies concerned over Russia's military resurgence in the wake of the 2008 Georgia war. The deal has garnered fresh controversy since the start of the Ukraine crisis.