Launch controllers destroyed an unarmed Minuteman 3 intercontinental ballistic missile over the Pacific Ocean early Wednesday when a problem was detected minutes after it blasted off for a reliability test, the Air Force said.

It was the second Minuteman 3 test problem this summer at Vandenberg Air Force Base, 130 miles northwest of Los Angeles.

The latest missile was launched from an underground silo at 3:01 a.m. and was destroyed five minutes later because of unspecified safety concerns.

The Air Force has about 450 ICBMs, which are designed to carry a nuclear warhead, on alert in and around Montana, North Dakota and Wyoming. The military regularly tests unarmed missiles to check reliability and accuracy.

Air Force controllers Wednesday detected "a flight anomaly and terminated the flight for safety reasons," said Col. Matthew Carroll, chief of safety for Vandenberg's 30th Space Wing.

"Established parameters were exceeded and controllers sent destruct commands," Carroll said in a statement. "When terminated, the vehicle was in the broad ocean area northeast of Roi-Namur."

Roi-Namur is an island in the northern part of the Kwajalein Atoll in the Marshall Islands, some 4,200 miles from Vandenberg.

There were no details on what went wrong, and a Vandenberg spokesman said there won't be any further information until Thursday. The Air Force said there will be an investigation.

The Minuteman program is part of the nation's strategic deterrent forces controlled by the Air Force Global Strike Command at Louisiana's Barksdale Air Force Base. A message seeking comment was left Wednesday for the program's director, Lt. Col. Ronald Watrous.

On June 22, an unarmed Minuteman 3 was launched on a test flight to the Marshall Islands atoll, and the ICBM's re-entry vehicle successfully reached its Kwajalein Atoll target. But a communications problem during the countdown forced the launch command to be issued by ground control rather than an airborne control system on an E-6B Mercury jet, the Air Force said.

The Minuteman 3 reaches a speed of 15,000 mph and has a range of more than 6,000 miles.

According to the Air Force and contractor Boeing Co., the first launch of the three-stage missile was in 1968. Deployment began in 1970 and production stopped in 1978, but since then, there have been major programs to upgrade the guidance technology, rocket motors and other elements of the weapon system.

Minuteman 3s are nearly 60 feet long with a 5½-foot diameter, and they weigh more than 79,000 pounds, according to the Air Force.

Unlike earlier ICBMs such as the Titan, which used liquid fuel, the Minuteman 3 burns solid propellant.

After blast-off, each stage falls away as its fuel is expended, leaving the re-entry vehicle to coast on a suborbital trajectory through space and then fall back through the atmosphere toward its target.