The Pentagon said that a test on Monday of a new tactic for intercepting missiles aimed at American cities was a success, in an exercise that appeared intended to simulate how the United States would defend against an adversary like North Korea.

The test, the first in nearly two years, was conducted over the Pacific Ocean. It fired two “interceptors” from Vandenberg Air Force Base in California against a mock warhead launched from Kwajalein Atoll in the Marshall Islands.

“The system worked exactly as it was designed to do,” Air Force Lt. Gen. Samuel A. Greaves, director of the Pentagon’s Missile Defense Agency, said in a statement. “This test demonstrates that we have a capable, credible deterrent against a very real threat.”

Evaluating the success of missile interceptions is difficult. In the past, the Missile Defense Agency has been accused of exaggerating its “kills” in order to quiet critics who say a 50 percent successful interception rate is far from satisfactory.