Russian President Vladimir Putin said on Monday that his US counterpart Donald Trump's statement that Washington would resume nuclear tests was a "serious problem", Reuters reported.
Late last month, Trump ordered tests of US nuclear weapons, saying the US could not lag behind Russia and China.
Russian Defense Minister Andrei Belousov told Putin that the US was strengthening its strategic forces and had plans to deploy weapons.
The Russian president on Monday ordered senior military and defense-related civilian officials to make proposals for possible nuclear tests in response to US statements. If other countries conduct similar tests, Moscow will respond accordingly, he stressed.