SEOUL, South Korea — North Korea said Monday the missile it launched over the weekend was a new type of “medium long-range” ballistic rocket that can carry a heavy nuclear warhead. A jubilant leader Kim Jong Un promised more nuclear and missile tests and warned that North Korean weapons could strike the U.S. mainland and Pacific holdings.

North Korean propaganda must be considered with wariness — Pyongyang has threatened for decades to reduce Seoul to a “sea of fire,” for instance — but Monday’s claim, if confirmed, would mark another big advance toward the North’s goal of fielding a nuclear-tipped missile capable of reaching the U.S. mainland. Some experts, including officials in Tokyo, estimate that Sunday’s launch successfully tested a new type of missile in Pyongyang’s arsenal.

The test is also an immediate challenge to South Korea’s new leader, Moon Jae-in, a liberal elected last week who expressed a desire to reach out to North Korea. Pyongyang’s aggressive push to boost its weapons program also makes it one of the Trump administration’s most urgent foreign policy worries, though Washington has struggled to settle on a policy.

North Korea’s official Korean Central News Agency called the missile a “new ground-to-ground medium long-range strategic ballistic rocket,” and said the “Hwasong-12” was “capable of carrying a large, heavy nuclear warhead.” Kim Jong Un witnessed the test and “hugged officials in the field of rocket research, saying that they worked hard to achieve a great thing,” according to KCNA.

The rocket, “newly designed in a Korean-style,” flew 787 kilometers (490 miles) and reached a maximum altitude of 2,111.5 kilometers (1,310 miles), the North said, and “verified the homing feature of the warhead under the worst re-entry situation and accurate performance of detonation system.”

South Korea’s Defense Ministry said more analysis is needed to verify the North’s claim on the rocket’s technological features. Spokesman Moon Sang Gyun said it’s still unlikely that North Korea has re-entry technology, which would return a warhead safely back into the atmosphere.

Japanese officials said Sunday the missile flew for half an hour and reached an unusually high altitude before landing in the Sea of Japan.

North Korea is not thought to be able yet to make a nuclear warhead small enough to mount on a long-range missile, though some outside analysts think they can arm shorter range missiles with warheads; each new nuclear and longer-range missile test is part of the North’s attempt to build a nuclear-tipped long-range missile.

Kim said the North would stage more nuclear and missile tests in order to perfect nuclear bombs needed to deal with U.S. “nuclear blackmail.”

State media paraphrased Kim as saying that “the most perfect weapon systems in the world will never become the eternal exclusive property of the U.S., … strongly warning the U.S. should not … disregard or misjudge the reality that its mainland and Pacific operation region are in (North Korea’s) sighting range for strike.”

The launch complicates the new South Korean president’s plan to talk to the North, and came as U.S., Japanese and European navies gather for joint war games in the Pacific.