Pyongyang, AP—North Korea said Saturday that it successfully test-fired a newly developed ballistic missile from a submarine in what would be the latest display of the country’s advancing military capabilities.

Hours after the announcement, South Korean military officials said the North fired three anti-ship cruise missiles into its eastern sea.

North Korean also said for the second straight day that it would fire without warning at South Korean naval vessels that it claims have been violating its territorial waters off the western coast of the Korean Peninsula. South Korea’s presidential Blue House held an emergency national security council meeting to review the threat and discuss possible countermeasures.

Experts in Seoul say the North’s military demonstrations and hostile rhetoric are attempts at wresting concessions from the United States and South Korea, whose officials have recently talked about the possibility of holding preliminary talks with the North to test its commitment to denuclearization.

“By raising tensions, North Korea is trying to ensure that it will be able to drive whatever future talks with the US and South Korea,” said Yang Moo-jin, a professor from the Seoul-based University of North Korean Studies.

Officials from rival South Korea previously had said that North Korea was developing technologies for launching ballistic missiles from underwater, although past tests were believed to have been conducted on platforms built on land or at sea and not from submarines.

Security experts say that North Korea acquiring the ability to launch missiles from submarines would be an alarming development because missiles fired from submerged vessels are harder to detect before launch than land-based ones. North Korea already has a considerable arsenal of land-based ballistic missiles and is also believed to be advancing in efforts to miniaturize nuclear warheads to mount on such missiles, according to South Korean officials.

North Korean leader Kim Jong Un personally directed the submarine test launching and called the missile a “world-level strategic weapon” and an “eye-opening success,” said the North’s official Korean Central News Agency, or KCNA. The report did not reveal the timing or location of the launch.

Kim declared that North Korea now has a weapon capable of “striking and wiping out in any waters the hostile forces infringing upon the sovereignty and dignity of [North Korea].”

The North’s state-run Rodong Sinmun newspaper published photos of a projectile rising from the surface and Kim smiling from a distance at what looked like a floating submarine.

The test might have taken place near the eastern coastal city of Sinpo, where satellite imagery in recent months, analyzed by a US research institute, appeared to have shown North Korea building missile-testing facilities and equipping a submarine with launch capabilities. In a separate report Saturday, KCNA said Kim visited a fisheries facility in Sinpo to offer “field guidance.”

South Korea’s defense ministry had no immediate comment on North Korea’s claim of a successful test.

Ministry officials have previously said that North Korea has about 70 submarines and appears to be mainly imitating Russian designs in its efforts to develop a system for submarine-launched missiles. North Korea is believed to have obtained several of the Soviet Navy’s retired Golf-class ballistic missile submarines in the mid-1990s.

Uk Yang, a Seoul-based security expert and an adviser to the South Korean military, said it is unlikely that the North possesses a submarine large enough to carry and fire multiple missiles. However, it is hard to deny that North Korea is making progress on dangerous weapons technology, he said.

The website 38 North, operated by the US-Korea Institute at the Johns Hopkins School of Advanced International Studies, said in January that such capability posed a potential new threat to South Korea, Japan and US bases in East Asia, although North Korea’s submarines tend to be old and would be vulnerable to attack.

Meanwhile, a South Korean Joint Chief of Staff official said the anti-ship cruise missiles were fired within a span of an hour early Saturday evening from an area near the eastern port city of Wonsan. The official, who didn’t want to be named, citing office rules, identified the missiles as KN-01 missiles, which the North also test-fired in February in an event personally attended by North Korean leader Kim.

There had been expectations that Kim would attend the Victory Day celebration in Russia on Saturday for his international debut, but North Korea sent to Moscow the head of its rubber-stamp parliament instead.