North Korean leader Kim Jong Un (L) guides artillery fire and landing exercises in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang February 21, 2015. REUTERS/KCNA/Files

By Andrea Shalal

WASHINGTON (Reuters) - The U.S. government believes North Korea has the capability to launch a nuclear weapon against the U.S. homeland and stands ready to defend against any such attacks, a high-level U.S. military official said on Wednesday.

Admiral Bill Gortney, commander of U.S. Northern Command and the North American Aerospace Defense Command, said he agreed with U.S. intelligence assessments that North Korea had nuclear weapons, as well as the ability to miniaturize them and put them on a rocket that could reach the United States.

"We assess that they have the capability to reach the homeland with a nuclear weapon from a rocket," Gortney told an event hosted by the Atlantic Council think tank.

Gortney said it was very difficult to predict the behavior of North Korean leader Kim Jong Un but the U.S. military was prepared to respond if he were to use a nuclear weapon.

"We’re ready for him, and we’re ready 24 hours a day if he should be dumb enough to shoot something at us," Gortney said.

"I'm pretty confident that we're going to knock down the numbers that are going to be shot."

North Korea's space agency said last month Pyongyang was building a new satellite and readying it for launch, with any use of a long-range rocket suggesting that the secretive state has made advances developing a ballistic missile. [ID:nL4N11L0SV]

North Korea says its rocket launches are part of a legitimate space programme aimed at putting satellites into orbit. It has in the past conducted missile tests in defiance of international warnings and sanctions.

The U.S. Missile Defense Agency said in March North Korea could achieve the ability to launch an intercontinental ballistic missile this year. [ID:nL2N0WK33E]

On Wednesday, Gortney said the U.S. military was investing to modernize its current missile defense system, add new sensors and radars to better identify potential missile launches, and drive down the cost of defending against such attacks.

He warned that the failure of the U.S. Congress to pass a budget for fiscal year 2016, or a resumption of mandatory budget cuts, could jeopardize the funding needed for such efforts.

(Editing by Paul Tait)