North Korea has threatened to retaliate against the US if Washington did not halt multinational military exercises scheduled to begin in South Korea on Monday, the media reported on Sunday.
A State Department official told CNN on Saturday that it was aware of the threats.
The military exercises were transparent, defence-oriented and designed to increase the readiness of South Korea and the region, the official said.
"These exercises are a clear demonstration of the US commitment to the alliance," the official said.
South Korea conducts the annual exercises with the US and forces from Australia, Canada, Colombia, Denmark, France, New Zealand and Britain. The exercises will conclude on August 28.
North Korea strongly opposes the joint exercises.
A North Korean media report said: "This is not the same old, ill-equipped North Korea that never could stand up to the US in the past. In fact, this year, they are threatening to attack the US on its own soil."