WASHINGTON • The Pentagon can defend against any North Korean missile threat, but Pyongyang's rapidly evolving weapons programme is shrinking the warning time ahead of a launch, says a top general.

General Lori Robinson said she was "extremely confident" of America's ability to intercept an intercontinental ballistic missile, if North Korean leader Kim Jong Un succeeds in developing the technology.

"Right now... he can't reach our homeland, but I am confident, should he do that," said Gen Robinson, who heads the North American Aerospace Defence Command, which provides missile detection and defence for the region.

On Wednesday, Pyongyang fired a ballistic missile into the sea between the Korean peninsula and Japan, the latest in a string of missile tests. The latest test came just ahead of US President Donald Trump's summit with Chinese President Xi Jinping.

The Pentagon said the extended- range Scud missile had an in-flight failure before crashing into the sea. Filled with liquid fuel, Scuds are harder to transport and prepare for launch than the more sophisticated solid-fuel rockets used by the US and other nations.

North Korea is now building and testing an intercontinental ballistic missile with a solid-fuel motor that could be carried by a small, easily hidden road convoy.

On Feb 11, Pyongyang said it had successfully tested a new ballistic missile powered by a solid-fuel engine. Such rockets are harder for existing technology to detect, Gen Robinson warned on Thursday.

"Amid an unprecedented pace of North Korean strategic weapons testing, our ability to provide actionable warning continues to diminish," she said in written testimony to senators.

She added that the US must continue to invest in the latest sensors and radar systems. "As adversaries continue to pursue credible and advanced capabilities, we too must evolve our missile defence capabilities to outpace increasingly complex threats."

AGENCE FRANCE-PRESSE