MOSCOW — A senior Russian diplomat says Washington's latest moves aimed at easing Moscow's concern about NATO's U.S.-led missile defense plans are insufficient.

Monday's statement by Deputy Foreign Minister Sergei Ryabkov followed an exchange of letters by President Barack Obama and Russia's President Vladimir Putin that mentioned the missile defense dispute, a longtime irritant in bilateral ties.

Russian media said Obama offered to provide Russia with more information about the missile defense plans.

The Kremlin has dismissed U.S. assurances that the shield is a defense against Iranian missiles and sought legally binding guarantees that it wouldn't be aimed against Russia.

Ryabkov told Voice of Russia radio that the latest U.S. proposals on missile defense are "concrete" and "serious," but Moscow still sees them as insufficient and wants more specific technical guarantees.