North Korea capped one of its busiest months of missile tests ever with the launch of its Hwasong-12 intermediate-range ballistic missile on Sunday, highlighting efforts to ensure it has reliable systems for delivering nuclear warheads.

January's testing schedule began with the launch of a new "hypersonic missile," and went on to include long-range cruise missiles, and short-range ballistic missiles launched from railcars and airports, underscoring the nuclear-armed state's rapidly expanding and advancing arsenal amid stalled denuclearization talks.

North Korea hasn't tested its longest-range intercontinental ballistic missiles (ICBMs) or nuclear weapons since 2017, but the Hwasong-12 launch signaled it could soon resume such testing, officials in South Korea and the United States said.