The U.S. government has accused Russia of conducting tests that violate a 1987 nuclear-missile treaty that Washington says is "a very serious matter."
A U.S. administration official said President Barack Obama notified Russian President Vladimir Putin about the charges in a letter on July 28.
The U.S. says Russia tested a new ground-launched cruise missile, breaking the Intermediate-Range Nuclear Forces Treaty that U.S. President Ronald Reagan signed with Soviet leader Mikhail Gorbachev some 27 years ago.
The treaty was designed to eliminate ground-launched missiles with 500 to 5,500 kilometer ranges.
The findings will be in a State Department report on arms-control treaty compliance due to be issued on July 29.
Washington has expressed concern over possible violations before, but this is the first time it has formally accused Russia of violating the treaty.
