Russia has denied for years it is developing any such missile, which is banned under the INF (Intermediate-range Nuclear Forces) Treaty.

(HT Remark: The fact that a US official would openly and publicly threaten Russia with a US Military attack upon Russian territory is one of the most staggering developments in this writer's 56 years on earth.  It is reckless, arrogant, and terrifying in its implications.)

The United States believes Russia is developing a ground-launched system in breach of the Cold War INF treaty that could allow Russia to launch a nuclear strike on Europe at short notice. The treaty bans medium-range missiles capable of hitting Europe or Alaska. The United States and Russia celebrated its 30th anniversary in Geneva in 2017.