An interceptor missile destroyed a mock warhead over the Pacific Ocean in a key test of the United States' missile defense system, officials said. It was the most realistic test of the systems that would be used against an attack, said Missile Defense Agency spokesman Rick Lehner. The 16-meter interceptor shot out of an underground silo at Vandenberg Air Force Base on the central California coast at 10:39 a.m. (1739 GMT) Friday, 17 minutes after the mock warhead was launched from Kodiak Island, Alaska, Lehner said. The interceptor carried a refrigerator-sized "kill vehicle" that locked on to the approaching mock enemy missile and flew into the 1-meter-long warhead at 29,000 kph. Lehner said both disintegrated more than 160 kilometers above the Earth and a few hundred kilometers west of Vandenberg. The interceptor's flight lasted 13 minutes. The test was designed to see whether the "kill vehicle" could get close to the warhead to test the tracking and sensor systems which would be used in an actual missile attack. Critics also argued early on that the demise of the Soviet Union made a full-scale missile attack on the US unlikely. Supporters say the US still is vulnerable to missiles from rogue states. In July, North Korea unsuccessfully test-fired a missile that was believed capable of reaching the northwestern US coast. On Monday, Defense Secretary Donald H. Rumsfeld visited Fort Greely in Alaska, where 11 interceptors are kept. Asked whether the missile shield was ready for use against a North Korean missile, Rumsfeld said he would not be fully convinced without more realistic testing. "A full end-to-end" demonstration is needed "where we actually put all the pieces" of the highly complex and far-flung system together, he said.