The commander heading up US military forces in South Korea has warned that if left unchecked, North Korea's capabilities will soon match its rhetoric.

Admiral Harry Harris was speaking in a prepared testimony to the House Armed Services Committee on 26 April about the current tensions between the US and North Korea.

"North Korea vigorously pursued a strategic strike capability in 2016," Harris said.

"Kim's strategic capabilities are not yet an existential threat to the US, but if left unchecked, he will gain the capability to match his rhetoric."

Both the US and North Korea have been engaging in test drills near the border.

Harris echoed President Donald Trump's stance that all options remain on the table for responding to the hermit state.

The administration "must consider every possible step to defend the US homeland and our allies", he said.

Harris also confirmed that it was not the ambition of the current administration to topple Kim's regime.

"In confronting the North Korean threat, it is critical that the US be guided by a strong sense of resolve both publicly and privately in order to bring Kim Jong Un to his senses, not his knees," Harris said.

Senators have been invited to a briefing on North Korea by top Trump administration officials on Wednesday afternoon at the White House, with Trump planning to drop by. House members will get a separate administration briefing at the Capitol later in the day.