By Roberta Rampton and Steve Holland
WASHINGTON (Reuters) - President Barack Obama wrote to Russian President Vladimir Putin to inform him directly that the U.S. government had determined that Russia violated the intermediate-range nuclear treaty, White House spokesman Josh Earnest said on Tuesday.
The United States is seeking high-level talks over what it said was an infraction of the Cold War-era treaty, ratified in 1988, which was designed to eliminate ground-launched cruise missiles with ranges of 500 to 5,500 km (310 to 3,400 miles).
Earnest declined to comment on how or when Russia violated the treaty, but said the United States is concerned in part about the risk of proliferation.
The fact that Obama raised the issue directly with Putin signals the gravity of the situation, Earnest told reporters at a briefing.
"That is an indication that this is a matter that merits the serious attention of the leaders of both the United States and Russia," Earnest said.
He said the administration has raised its concern with Russia about the violation "on a number of occasions." "It is fair for you to conclude that their response to our concerns was wholly unsatisfactory, and that is why additional talks are merited," Earnest said.
(Additional reporting by Eric Beech; Editing by Will Dunham, Doina Chiacu)