"Our assessment is that they have the ability to put a nuclear weapon on a KN-08 and shoot it at the homeland," Gortney said. "That is the way we think, and that's our assessment of the process."
"We haven't seen them test the KN-08 yet and we're waiting for them to do that, but it doesn't necessarily mean that they will fly it before they test it," he added.
North Korea has conducted three nuclear tests since 2006, none involving the KN-08. But even without seeing a test of a nuclear-capable KN-08, Gortney said it would be "prudent" to plan for the threat.
On Tuesday, Gortney said that if North Korea were to fire a missile at the US, “I am confident we can knock it down.”
— Sputnik (@SputnikInt) April 8, 2015
That contrasts the testimony he gave during a congressional hearing last month, when he said that the KN-08’s mobility “will complicate our ability to provide warning and defense against an attack.”
"It's not that hard to shrink it down,” Lewis said, “but what happens is you start to encounter reliability problems, especially if it's got a ride on an ICBM."
Gortney’s comment comes as US Secretary of Defense Ashton Carter plans to visit Seoul on Thursday for talks on ways to bolster deterrence against North Korea.
Those talks, Carter said in a Monday speech, will "reinforce deterrence and improve capabilities on the peninsula to counteract an increasingly dangerous and provocative North Korea."
After its last nuclear test in 2013, North Korea claimed that it had the ability to hit the mainland US with nuclear-tipped missiles. It also defied United Nations Security Council resolutions by test-firing ballistic missiles.