Washington has dismissed a threat by North Korea that it will launch a nuclear strike against the US in the event of an American attack against it.
The Taepodong missile could reach Alaska (archive picture)
A White House spokesman described the threat as "deeply hypothetical".
Tony Snow said the statement was about what might happen if something that had not happened, did happen.
He urged the North Koreans to return to six-party talks aimed at curbing the country's nuclear activities. The talks stalled last year.
Earlier on Monday, Pyongyang warned it would launch an "annihilating" nuclear strike if its atomic facilities were pre-emptively attacked by the United States.
But the US State Department said it had no intention of attacking North Korea.
"The strong preference of the United States and the other parties to the six-party talks, other than North Korea, is for North Korea to rejoin the talks, to sit down at the table," Mr Snow said.
The talks involving the US, Russia, China, Japan, South Korea and North Korea stalled in November after Pyongyang objected to military drills conducted by the US and South Korea, which it denounced as a preparation for invasion.
North Korea is thought to be preparing to launch the Taepodong-2 from the Musudan-ri launch site in the northeast of the country.
The untested missile has a range of up to 6,000 km (3,730 miles), putting parts of the US within striking distance.
The last time North Korea tested a long-range missile was in 1998, when it launched a Taepodong-1 over northern Japan.