VANDENBERG AIR FORCE BASE, Calif. (AP) – The U.S. has test-fired an intercontinental ballistic missile from California for the second time in seven days.

The Air Force says an unarmed Minuteman 3 blasted off from a silo at Vandenberg Air Force Base Wednesday morning and delivered a mock warhead to a target at Kwajalein Atoll in the Pacific Ocean after a 4,000-mile flight.

The test of the nuclear missile took 10 months to plan. Another Minuteman 3 was launched from the same base exactly a week earlier.

The U.S. has about 450 of the missiles and they are routinely tested. But the latest tests come amid rising tensions with North Korea, which has tested its own nuclear missiles – including some designed to reach the United States.

The U.S. has sent warships to the region to deter that country from conducting such tests.