The threat of such a test, coming amid plans to test a controversial rocket this week, is seen as an effort by North Korea to extort more aid from the international community.
Washington is likely to take the matter to the UN Security Council, analysts say, and could tighten its already tough sanctions.
President Obama's admonition against firing a long-range rocket next month went unheeded by North Korea, which argued it is for economic development. Will China and Russia have any sway?
Though North Korea wasn't mentioned by name, the impoverished nation's recent rocket tests cast a shadow over the nuclear proliferation summit in Seoul.
On a trip to South Korea, President Obama visits the heavily-armed DMZ and warns the regime across the border not to test a long-range missile next month.
More than 50 world leaders, including President Obama, are set to arrive in Seoul to discuss prevention of nuclear terrorism, but Pyongyang's plans for a new missile test have shifted the discussion.
North Korea says it wants to peacefully use space. Analysts say the regime wants to test a missile that could deliver a nuclear warhead to the US.
The US will not supply food aid to a hunger-stricken North Korea if Pyongyang persists in its plan to launch a long-range missile next month, the State Department warned late Friday.
North Korea's announcement that it would launch a long-range missile carrying a satellite throws into doubt the future of a food-for-nuclear-moratorium deal with the US.
North Korea announced plans to launch a satellite atop a ballistic missile. The US says North Korea would be violating a UN resolution.