WASHINGTON (Reuters) - The United States will start initial production on parts for ground-launched cruise missile systems, the Pentagon said on Monday, after Washington announced it plans to withdraw from the Intermediate-Range Nuclear Forces Treaty.

A tomahawk cruise missile launches from the Arleigh Burke-class guided-missile destroyer USS Shoup for a live-fire exercise during Valiant Shield 2018 in the Philippine Sea, September 18, 2018. REUTERS/U.S. Navy/Mass Communication Specialist 2nd Class William Collins III/Handout

Last month, the United States announced it would withdraw from the INF Treaty in six months unless Moscow ends what Washington says are violations of the 1987 pact.

Russia announced it was suspending the treaty. Moscow denies flouting the accord and has accused Washington of breaking the accord itself, allegations rejected by the United States.

“We will commence fabrication activities on components to support developmental testing of these systems - activities that until February 2 would have been inconsistent with our obligations under the Treaty,” said Army Lieutenant Colonel Michelle Baldanza, a Pentagon spokeswoman.

“This research and development is designed to be reversible, should Russia return to full and verifiable compliance before we withdraw from the Treaty in August 2019,” Baldanza said.

The Pentagon said the efforts would be conventional and not nuclear.

The INF treaty required the parties to destroy ground-launched ballistic and cruise missiles with ranges of between 500 and 5,500 km (310 to 3,420 miles).

The United States alleges a new Russian cruise missile violates the pact. The missile, the Novator 9M729, is known as the SSC-8 by the North Atlantic Treaty Organization.

Speaking at a Washington conference, Russian Ambassador to the United States Anatoly Antonov dismissed allegations that the missile violated the treaty as a “fairy tale.”

In January, the head of Russia’s military’s missile and artillery forces said the missile’s maximum range fell short of the treaty’s lower limit.

Frank Rose, a former U.S. assistant secretary of state for arms control now at the Washington’s Brookings Institution think tank, suggested the Pentagon announcement may be designed to pressure Russia to return to compliance with the treaty.

“My best guess is that it is political signaling intended to make it clear the United States is serious about moving forward with the development of a new GLCM (ground-launched cruise missile) unless Russia returns to compliance with the treaty,” Rose said.

The United Nations has urged the United States and Russia to preserve the treaty, saying its loss would make the world more insecure and unstable.