North Korea successfully conducted an underwater test-fire of a newly developed strategic ballistic missile from a submarine, in what is viewed as Pyongyang’s latest attempt in its pursuit of advancing military capabilities, state media reported Saturday. The report came a day after North Korea’s military threatened to launch “targeted strikes” against South Korea’s navy, accusing it of violating territorial waters off the western sea border.

North Korean leader Kim Jong Un attended the test launch as the submarine plunged into the water and, after a while, “the ballistic missile soared into the sky from underwater,” the official KCNA news agency reported. Kim, who praised the test launch as an “eye-opening success,” described the missile as a “world-level strategic weapon.”

The missile is “capable of striking and wiping out in any waters the hostile forces infringing upon the sovereignty and dignity of” North Korea, KCNA quoted Kim as saying.

Although the report did not reveal the exact timing and location of the test, a separate KCNA report said Saturday that Kim had given field guidance at a fishery complex in Sinpo, a port city on North Korea’s east coast and the location of a known submarine base, Reuters reported.

Despite being under United Nations sanctions that ban the country from developing or using ballistic missile technology, North Korea is believed to be working on the missile-launch capability for its submarines. In January, researchers at Johns Hopkins University’s U.S.-Korea Institute said on its website 38 North that satellite imagery showed evidence of work on vertical launch tubes on a submarine for either ballistic or cruise missiles.

“North Korea’s development of a submarine-launched missile capability would eventually expand Pyongyang’s threat to South Korea, Japan and U.S. bases in East Asia, also complicating regional missile defense planning, deployment and operations,” according to the report on 38 North. “Nevertheless, such a threat is not present today. Moreover, an effort by Pyongyang to develop an operational missile-carrying submarine would be an expensive and time-consuming endeavor with no guarantee of success.”

Meanwhile, experts in Seoul and Washington said that North Korea has been developing a submarine-launched ballistic missile, which could weigh about 2,500 ton, South Korea’s Yonhap news agency reported, adding that the missile can be a new threat to the security of the Korean Peninsula.

On Friday, North Korea’s military warned of “unannounced targeted strikes” against South Korea’s navy, accusing it of crossing its western sea border two to three times a day between May 1 and May 7. In a statement, carried by KCNA, North Korea also threatened to launch stronger attacks on South Korean ships if Seoul retaliates.

In March, North Korea reportedly test-fired seven surface-to-air missiles off its east coast. The test came as the U.S. and South Korea finished the first of two large-scale annual military exercises.

In April, North Korea test-fired four short-range ballistic missiles about 84 miles into the ocean off its west coast. The test-fire came one week before U.S. Defense Secretary Ashton Carter was scheduled to travel to South Korea for a three-day summit to evaluate the nation’s defense capabilities.