Moscow's participation in the European missile defense is the best way to ease Russia's concern about the project, a high-ranking U.S. Department of State official told RIA Novosti on Tuesday.

"As we have said previously, our missile defenses are not directed at Russia nor do they threaten Russia's strategic deterrent. We believe that cooperation is the best way for Russia to gain confidence that U.S. missile defenses are not directed at it," the State Department source told RIA Novosti on the condition of anonymity.

The statement comes shortly after Russian Deputy Foreign Minister Sergei Ryabkov expressed his concern about the U.S. refusal to provide legally binding guarantees that its European missile defense system will not be directed against Russia, and warned that Moscow may pull out of the new START Treaty in response.

Another State Department source expressed hope that the dialog with Moscow on the issue will continue.

"We do not negotiate in the media and Under Secretary Tauscher looks forward to continuing her conversations with her counterparts on this subject," the source said.

WASHINGTON, May 17 (RIA Novosti)