US Defence Secretary Robert Gates says North Korea is likely to launch a rocket soon, and Washington would not attempt to stop it, BBC reported.
North Korea has said it will launch a satellite into orbit next month.
South Korea, Japan and the US say the launch is cover for a test of the Taepodong-2 ballistic missile.
Japan had said earlier it would deploy missile interceptors to destroy any parts of a North Korean rocket that might fall on its territory.
North Korea has said it would regard any rocket intercept as an act of war.
But Mr Gates said the US would not attempt to shoot it down.
"I would say we're not prepared to do anything about it," he told Fox News Sunday.
"If we had an aberrant missile, one that looked like it was headed for Hawaii, we might consider it, but I don't think we have any plans to do anything like that at this point," said Mr Gates.
The US had previously said the launch would violate UN Security Council resolutions, while Russia has said North Korea should "abstain" from testing any missiles.
North Korea says it intends to test-fire the rocket between the 4 and 8 April.
The trajectory issued by Pyongyang shows the rocket will pass over Japan, with the first booster stage landing in the sea to the west, the second in the Pacific Ocean to the east.
Japan's interception is only likely to be activated if the launch does not go as planned and debris appears to be falling towards Japan.