SEOUL, South Korea (AP) — North Korea says it has successfully conducted an engine test of a new intercontinental ballistic rocket it claims will strengthen its ability to stage nuclear strikes on the United States.

The North's official Korean Central News Agency released the news Saturday.

The move, if true, would be a big step forward for the North's nuclear weapons program. But South Korean officials still say North Korea doesn't yet have a reliable intercontinental ballistic missile, let alone the ability to arm it with a nuclear warhead.

The North has threatened pre-emptive nuclear strikes against Washington and Seoul and fired short-range missiles and artillery into the sea in an apparent response to ongoing U.S.-South Korean military drills and tough U.N. sanctions imposed over an earlier nuclear test and long-range rocket launch.