Marine Le Pen, leader of France's National Front, attacked the French government's decision to suspend delivery of a first warship to Russia, saying on Thursday it had acted against the national interest and caved in to U.S. pressure.

Le Pen, whose extreme-right party has been winning voters from mainstream political groups of both left and right, has been a fierce critic of the West's policy towards Russia in the Ukraine conflict, which she sees as overly hostile to Moscow.

On the eve of a NATO summit, President Francois Hollande's office said on Wednesday France would hold off on delivery of a first helicopter carrier, slated for October. It accused Russia of actions in Ukraine which ran "against the foundations of security in Europe."

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For months he had resisted pressure from Washington and other allies to make the move. France had argued that other countries must share the burden in imposing a new round of sanctions on Russia and that any measures should also include the energy and financial sectors as well as defense.

"This decision is very serious, firstly because it runs contrary to the interests of the country," Le Pen told RTL Radio, noting that French jobs would be at risk and France would have to pay a fine if it failed to deliver the warships.

Le Pen, whose National Front was the largest French party in European Parliament elections this year as unemployment reached record levels, said the decision "reveals our subservience to American diplomacy."

Four hundred Russian sailors have been training to operate the carrier since the end of June in shipyards at Saint-Nazaire, on France's Atlantic coast.

Signed by former president Nicolas Sarkozy's conservative government, the 1.2 billion euro ($1.58 billion) contract for two warships was the first by a NATO member country to supply Russia with military equipment.

As recently as July, Hollande said France would honor the contract for the first carrier, but that he was prepared to review a second due to be delivered in 2016.