UPDATE 3-U.S. to announce suspension of compliance with nuclear pact -officials

The United States will announce plans to suspend compliance with a landmark nuclear pact with Russia, a move triggering a six-month clock that could lead to its withdrawal from the arms control accord, U.S. officials said. It was conceivable, however, that Washington could choose not to pull out of the Intermediate-range Nuclear Forces Treaty, if Russia came into compliance with the 1987 arms control accord in that period.

The United States alleges that a new Russian missile, the Novator 9M729, called the SSC-8 by NATO, violates the pact, which bans either side from stationing short- and intermediate-range, land-based missiles in Europe. Russia denies that, saying the missile’s range puts it outside the treaty, and it has accused the United States of inventing a false pretext to exit a treaty Washington wants to leave anyway so as to develop new missiles. Russia has also rejected a U.S. demand to destroy the new missile.

"We’re going to announce suspension," a U.S. official told Reuters on condition of anonymity. A second U.S. official said the U.S. action "is reversible" if Russia comes back into compliance during the six-month U.S. suspension. "Then the U.S. would unsuspend," the official said.

The dispute over the treaty is aggravating the worst U.S.-Russia frictions since the end of the Cold War in 1991. Some experts believe the treaty's collapse could undermine other arms control agreements and speed an erosion of the global system designed to block the spread of nuclear arms. (Reporting by Steve Holland, Jonathan Landay and Lesley Wroughton; Editing by Leslie Adler)