Accusing Russia of "sustained and repeated violations" of the Intermediate-Range Nuclear Forces (INF) treaty, Defense Secretary Mark Esper said the US had already begun work to develop "mobile, conventional, ground-launched cruise and ballistic missile systems."

As the United States had "scrupulously complied" with its obligations to the 1987 treaty until its formal withdrawal, "these programs are in the early stages," Esper said in a statement.

"Now that we have withdrawn, the Department of Defense will fully pursue the development of these ground-launched conventional missiles as a prudent response to Russia's actions.

"The Department of Defense will work closely with our allies as we move forward in implementing the National Defense Strategy, protecting our national defense and building partner capacity," he added.

Moscow has said that Washington is making a "serious mistake" pulling out of the treaty, insisting that the US had abandoned the agreement for its own gain rather than because of alleged Russian violations.