SEOUL, South Korea >> The United States, South Korea and Japan conducted a joint missile defense exercise on Monday aimed at countering North Korea’s growing nuclear arsenal, as a top North Korean army official warned the U.S. that it risks “a clearer security crisis and insurmountable threats.”

Last week, North Korea conducted one of its most provocative weapons demonstrations in years by flight-testing for the first time an intercontinental ballistic missile powered by solid fuel. It is considered a more mobile, harder-to-detect weapon and could directly target the continental United States.

South Korea’s navy said Monday’s three-way drills took place in international waters off the country’s eastern coast and focused on mastering procedures for detecting, tracking and sharing information on incoming North Korean ballistic missiles. The one-day naval exercise involved an Aegis destroyer from each country.

– The Associated Press