VANDENBERG AIR FORCE BASE, Calif. -- The U.S. Air Force launched an unarmed intercontinental ballistic missile from a California base on Wednesday, a month after the test flight was postponed because of tensions with North Korea.

The Minuteman 3 lifted off at 6:27 a.m. PDT (1327 GMT) Wednesday from Vandenberg Air Force Base. It splashed down less than 30 minutes later and 4,000 miles (6,400 kilometres) away at the Kwajalein Atoll in the Pacific Ocean, Air Force officials said.

It was the first Minuteman test-launch of 2013. Several missiles are launched from Vandenberg each year to verify the weapon system's accuracy and reliability.

The original mid-April flight was postponed by Defence Secretary Chuck Hagel amid concerns that it might be misinterpreted during a time of heightened tension with North Korea.

The launch was rescheduled for Tuesday morning but was pushed back a day due to a problem with range safety instruments.

The U.S. has 450 nuclear-armed Minuteman 3 missiles ready for combat use, if directed by the president. They are in underground silos in five states.