North Korea said Saturday that it had successfully test-fired a submarine-launched ballistic missile from under the sea, which would mark a major advance in its military capabilities.

Kim Jong Un, the North Korean leader, ordered the test of the “world-level strategic weapon” and was present when it “soared into the sky from underwater,” the state-run Korean Central News Agency reported. The Rodong Sinmun, the mouthpiece of the Korean Workers’ Party, separately ran photos that showed Kim on a boat holding binoculars as the rocket blasted out of the sea.

North Korea had previously tested the missile from platforms on land and at sea, but this appears to be the first time it has launched a rocket from under water. South Korean officials later said it appeared that the North fired three anti-ship cruise missiles.

If the missile technology could be deployed by the North Korean Navy, analysts said it could pose a threat to South Korean and U.S. Navy vessels in the area, but that is still a big if.

The North Korean reports did not say when or where the test took place, or how far the missile flew. There was no independent confirmation of the reports.

But the test “proved and confirmed that the ballistic missile fire from the submarine fully met the requirements of the latest military science and technology,” KCNA said, according to a translation by NK News.

News of the launch came on the same day that Kim had been expected to make his first foreign appearance, at Russia’s World War II Victory Day celebrations in Moscow.

But the Kremlin last week said Kim would not be attending because he had to take care of “internal matters.” Saturday’s photos show Kim instead flexing his military muscle at home, declaring the test an “eye-­opening success.”

The test also comes after days of saber-rattling by the North, which has said it would fire at South Korean naval vessels that it deemed to have entered its territorial waters. The two Koreas has been arguing over its disputed western sea border.

Daniel Pinkston, the Korea analyst at the International Crisis Group and a non-proliferation expert, said that he doubt the launch reported Saturday was actually from a submarine.

"I think they probably launched it from some kind of submerged platform, possibly towed by a submarine. I think it would be too risky to do the first launch from a submarine," he said. North Korea has a limited fleet of aging subs.

While the launch was a significant step for North Korea, Pinkston said he did not think the system was operational yet. "That will still take time and more flight-tests. Now we can watch the responses. I don't see [North] Korea's neighbors sitting around and not responding," he said.

South Korea and the United States have been concerned that North Korea was developing a ballistic missile that could be launched underwater. They are also concerned that North Korea might be making progress on miniaturizing a nuclear weapon so that it could be attached to a missile, although there has been no evidence that it has mastered this difficult step.

Pyongyang has previously said that it has tested a missile launcher from the shore in Sinpo, on North Korea’s east coast, and in February said that it had from the test of a canister-mounted anti-ship cruise missile from a patrol vessel., a defense analysis Web site, reported this week that North Korea had conducted a test from an underwater test platform near Sinpo, quoting U.S. defense officials as saying that the development was part of North Korea’s efforts to expand the country’s nuclear-weapons capacity.

“The submarine can get the platform to launch the missile within range of the continental United States, Alaska, or Hawaii,” it quoted Bruce Bechtol, a former Defence Intelligence Agency official, as saying. “Thus, once operational, this immediately brings key nodes in the United States within range of what would likely be a nuclear armed missile.”