Jim Michaels

USA TODAY

The U.S. military on Tuesday successfully intercepted an intercontinental-range missile for the first time, a key test of its missile-defense system amid heightening tensions with North Korea.

The successful test represented a "critical milestone" for the Pentagon's defensive missile system, said Navy Vice Adm. Jim Syring, director of the Missile Defense Agency.

The interceptor was launched from a silo at Vandenberg Air Force Base in California and hit the test missile fired from Kwajalein Atoll in the Pacific, the Missile Defense Agency said.

The test was a major challenge because an intercontinental ballistic missile flies faster than a shorter-range missile.

Prior to Tuesday, the U.S. military had conducted 17 tests of its missile-defense system and nine were successful.

North Korea’s nuclear ambitions have injected a new sense of urgency to building an effective defense against the country and actions of its unpredictable leader, Kim Jong Un, who is trying to develop a long-range missile capable of carrying a nuclear warhead and reaching the U.S. mainland. President Trump has vowed to prevent that from happening and has leaned on China, North Korea's closest ally, to use political and economic leverage to persuade Kim to halt his weapons program.

On Monday, North Korea tested a short-range missile that flew about 280 miles before landing in the Sea of Japan.

It was the latest in a recent string of North Korean missile tests, including two that exploded shortly after launch. The country hasn’t yet developed a missile capable of reaching the U.S. mainland, but the U.S. government believes the continual testing is bringing North Korea closer to that goal. “We always assume that with a testing program they get better with each test,” Defense Secretary Jim Mattis told CBS News on Sunday.

During the U.S.-Soviet Cold War era, President Ronald Reagan vowed to develop a missile defense that became known as "Star Wars," because it involved a satellite-based system. But technological progress was slow and opponents warned that an effective defense against the Soviets' massive intercontinental missile arsenal might invite a first-strike before a system was perfected.

A defensive system "is not something we had developed on par with our offensive capabilities,” said David Maxwell, associate director of the Center for Security Studies at Georgetown University. “It’s much easier to launch a missile than it is to shoot one down.”