Russia says a U.S. plan to deploy naval missile interceptors off the Spanish coast is “unacceptable” and “cannot fail to cause concern.”

The U.S. plans to deploy four Aegis cruisers as part of NATO's anti-ballistic missile defense system. Its goal is to protect European NATO states and the United States from long-range missile attacks from countries such as Iran.

But Russia's Foreign Ministry said Thursday the deployment brings about “a significant build-up of U.S. anti-missile capabilities in Europe.” The ministry is concerned the system could undermine Russia's security if the weapons can be targeted against Russian strategic nuclear forces.

The Foreign Ministry also said it saw no sign that the U.S. would address Russia's desire for legal guarantees that the NATO system would not be aimed at Russia. It added that if events continue along the same path, NATO will miss “the opportunity to turn missile defense from an area of confrontation into a subject of cooperation.”

Romania, Poland and Turkey have previously declared their intention to join the U.S. missile shield in Europe.