US Secretary of State John Kerry reiterated Washington's opposition to France's sale of warships to Russia during a meeting with French counterpart Laurent Fabius earlier this week, US officials said Thursday.

Under a 1.2-billion-euro ($1.6 billion) deal agreed in 2011, France is to sell two Mistral-class helicopter carriers to Russia, despite criticism from several allies.

The issue has strained relations between the United States and France and was prominent during Fabius's visit to Washington this week.

US State Department spokeswoman Marie Harf confirmed on Thursday that Kerry and Fabius had discussed the sale during their meeting.

"We've expressed our concerns to the French government several times over this sale and don't think it's an appropriate time to move forward on such military sales given Russia's actions that we've seen recently to destabilize its neighbors," Harf said, referring to the ongoing crisis in Ukraine.

Fabius on Tuesday defended the sale, 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.

"France needs firmness lessons from absolutely no one," Fabius said.

"France will do its duty, whether in regard to Ukraine or elsewhere.

"The rule with contracts is that contracts which have been signed are honored."