Moscow says US strategic bombers rehearsed launching a nuclear attack on Russia earlier this month, amid heightened military activity near Russian borders.
Russian Defense Minister Sergey Shoigu said on Tuesday, "Ten strategic bombers practiced the option of using nuclear weapons against Russia almost simultaneously from the Western and Eastern directions," according to a Defense Ministry statement.
"The minimum proximity to our state border was 20 km," he added.
Shoigu said that Moscow had noted a significant increase in activity by US strategic bombers, which he said had carried out 30 flights close to Russia this month. That, he said, was 2.5 times more than the same period last year.
"In the course of these activities, US bomber crews conduct practice approaches to cruise missile firing points with subsequent mock missile strikes," Shoigu said.
He said Russian air defense units had taken unspecified measures to avoid any incidents during the activities.
US bomber flights close to Russia's eastern borders came during US military exercises,dubbed "Global Thunder," against which Russian President Vladimir Putin had warned last week. Putin said at the time that Western strategic bombers were carrying "very serious weapons" close to Russia. He said the West was taking Moscow's warnings not to cross its red lines too lightly.
The activities come at a time of high tensions between Washington and Moscow over Ukraine. Kiev and Washington accuse Moscow of planning an attack on its southern border, an allegation Russia denies as "absurd."
Russia also accuses the United States, NATO, and Ukraine of provocative and irresponsible behavior, amid Kiev's military build-up near the border with Russia.
On Tuesday, Kiev received two refitted former US coast guard patrol boats at the Ukrainian Black Sea port of Odessa, according to the Ukrainian navy.