President Donald Trump on Tuesday said the US will halt "war games" with its security ally Seoul, but he did not make clear when the freeze on the "provocative" exercises would kick in.

"Major military exercises have been suspended indefinitely on the Korean peninsula," the official said.

America has about 28,500 troops based in South Korea and they routinely train with their local counterparts.

Ulchi Freedom Guardian, which ordinarily starts in August, is a two-week drill based on a computerized command-and-control exercise.

Pyongyang considers it a highly provocative rehearsal for invasion.

Following last year's drills, the North fired ballistic missiles over Japan, triggering global alarm and a furious response from Tokyo.

The Pentagon did not immediately comment.