North Korea has a large number of "theater-class" missiles with a desire to develop a "credible" missile threat, a US commander has said, casting the recalcitrant regime as a strategic security challenge.

Adm. Charles Richard, head of the US Strategic Command (USSTRATCOM), made the assessment in a written statement to the House Appropriations Subcommittee on Defense prior to a closed-door hearing on Tuesday (US time).

"The DPRK previously tested ICBM class missiles designed to reach the US, and they have a large arsenal of theater-class missiles," he said, referring to the North by its official name, the Democratic People's Republic of Korea. "The recent missile launches demonstrate their ongoing desire to develop a credible missile threat."

Theater-class missiles refer to those intended for use in specific areas of military operations.

Richard's remarks came as Seoul and Washington are cranking up security cooperation in the wake of a series of North Korean missile launches, including the regime's March 24 test of an intercontinental ballistic missile (ICBM).

The commander reiterated the US' commitment of "extended deterrence" to its two key Asian allies, South Korea and Japan.

Extended deterrence means America's stated pledge to use a full range of military assets, both nuclear and conventional, to defend its allies.

The admiral also said that his command supports the Pentagon's efforts with regional partners to reduce military tensions and encourage diplomatic efforts to pursue the North's denuclearization. (Yonhap)