The United States announced Wednesday that a planned test of an unarmed intercontinental ballistic missile had been called off before launch, adding that an investigation was under way to determine what went wrong.The US Air Force said in a statement that it was assessing its options to reschedule the launch, one of a series of regular tests aimed at demonstrating the effectiveness of Washington’s nuclear arsenal and reassuring America’s allies.”An unarmed Minuteman III intercontinental ballistic missile test launch from Vandenberg Air Force Base, California, experienced a ground abort prior to launch,” the statement said. “The cause of the ground abort is currently under investigation.”The statement does not say where the land-based, long-range missile was to have ended up, but such test launches are generally aimed in the direction of the Marshall Islands, and the missiles typically go into the sea.The Minuteman III has been in service for 50 years, and is the only land-based ICBM in the US nuclear arsenal since 2005. The missiles are housed in silos on three US military bases in Wyoming, North Dakota and Montana. The US arsenal also includes Trident submarine-launched ballistic missiles and nuclear weapons carried by strategic bomber aircraft.