An undated photo released by the official Korean Central News Agency on Aug. 25 shows North Korean leader Kim Jong Un monitoring the test-fire of a strategic submarine-launched ballistic missile. (KNS/via AFP/Getty Images)

North Korean leader Kim Jong Un boasted about “the greatest success” of a ballistic missile launched from a submarine this week, which appeared to be a major technological breakthrough for the nuclear-armed nation.

After a series of flops, North Korea launched a missile from a submarine near its east coast port of Sinpo early Wednesday. It flew about 300 miles before falling into the sea inside Japan’s air defense identification zone, the area in which Tokyo controls aircraft movement.

The launch, apparently of a KN-11 or “North Star” missile, contravenes U.N. resolutions and was roundly condemned by Japan, South Korea and China, as well as by the United States and the United Nations.

But in North Korea’s state news media Thursday, the apparently successful launch was cause for major celebration. The Rodong Sinmun, the newspaper of the ruling Korean Workers’ Party, carried seven color photos on its front page Thursday, including a large one of Kim surrounded by military officials, all of them smiling broadly.

Such images are used in North Korean propaganda in an effort to convince the populace, who have little, if any, access to outside information, that their impoverished and technologically backward country is strong and standing up to a United States that, the state media say, is trying to destroy North Korea.

Kim lauded the missile launch as “a great manifestation and demonstration of the tremendous power and inexhaustible muscle,” according to the state-run Korean Central News Agency.

North Korea has “joined the front rank of the military powers fully equipped with nuclear attack capability,” and the U.S. mainland is now within North Korea’s striking range, he said.

The missile was launched at a steep angle, a South Korean military source told Yonhap News Agency in Seoul, and probably could have traveled for more than 600 miles if it had been fired at a regular angle.

The launch coincided with the start of annual drills between the South Korean and U.S. militaries, exercises that always elicit an angry reaction from the North, which views them as a pretext for an invasion. The young North Korean leader came out with another round of bluster Thursday.

“I do not guess what ridiculous remarks the U.S. and its followers will make about this test-fire, but I can say their rash acts will only precipitate their self-destruction,” Kim reportedly said.

The military has also clearly been trying to advance its ballistic missile program, conducting a series of land- and sea-based tests over the past year. It appears to be trying to work on its intermediate-range Musudan missile, which can theoretically reach Guam, and its submarine-launched missiles, which would give it the ability to stage an attack from sea.

The tests have had a patchy record of success. The most recent KN-11 launches — three in the past year — were all deemed failures because the missiles exploded at launch or traveled only a short distance.

But analysts say that even failures offer lessons for North Korea’s rocket scientists.

Joseph S. Bermudez, a military analyst affiliated with the Washington-based U.S.-Korea Institute at SAIS, said this week’s test showed that North Korea remains strongly committed to the long-term development of an operational submarine-launched ballistic missile (SLBM) and is learning from its previous successes and failures.

“Assuming the current rate of development, while North Korea still faces significant technological challenges including building a new class of submarine to carry the missile, it is on track to develop the capability to strike targets in the region — including Japan — by 2020,” Bermudez said in a commentary posted on the 38 North website.

The latest launch was widely condemned.

Stéphane Dujarric, spokesman for U.N. Secretary General Ban Ki-moon, said North Korea’s defiance of the international community was “deeply troubling.”

The foreign ministers of Japan, South Korea and even China, North Korea’s main ally, said after a meeting in Tokyo that the launch was “totally unacceptable.”