The rival Koreas have test-launched ballistic missiles hours apart in a display of military assets amid a faltering diplomatic push to strip North Korea of its nuclear programme.

South Korea’s presidential office said it conducted its first underwater-launched ballistic missile test on Wednesday afternoon. It said a domestically built missile fired from a 3,000-ton submarine flew a set distance before hitting a designated target.

The statement said the weapon is expected to help Seoul deter potential external threats, boost its self-defence and promote peace on the Korean peninsula.

South Korea's test-fires its first underwater-launched ballistic missile from a submarine
South Korea test-fires its first underwater-launched ballistic missile (South Korea Defence Ministry via AP)

The test followed two short-range North Korean ballistic missile launches detected by South Korea’s military, which in turn came after Pyongyang said on Monday that it had fired a newly developed cruise missile in its first weapons test in six months.

Experts say the North Korean launches showed it is pressing ahead with its arms build-up while trying to apply pressure on the US to resume stalled nuclear talks.

It is not usual for South Korea to publicly disclose high-profile weapons tests that some experts say could provoke the North unnecessarily. Observers say President Moon Jae-in’s government, which has been actively pursuing reconciliation with North Korea, may be responding to criticism that it is too soft on its neighbour.

Japan Koreas Tensions
A TV screen showing North Korean leader Kim Jong Un (Koji Sasahara/AP)

South Korea’s military said the North Korean missiles, launched from central North Korea on Wednesday, flew about 500 miles before landing in water between the Korean peninsula and Japan.

The US Indo-Pacific Command said the launches, while highlighting the destabilising impact of North Korea’s illicit weapons programme, did not pose an immediate threat to “US personnel or territory, or to our allies”.

Japanese Prime Minister Yoshihide Suga said: “The firings threaten the peace and safety of Japan and the region and are absolutely outrageous.

Koreas Tensions
A South Korean news report about North Korea’s missiles (Lee Jin-man/AP)

“The government of Japan is determined to further step up our vigilance and surveillance to be prepared for any contingencies.”

Japan’s coastguard said no ships or aircraft reported damage from the missiles.

Wednesday’s launches were a violation of UN Security Council resolutions that bar North Korea from engaging in any ballistic missile activities, but the council does not typically issue fresh sanctions on Pyongyang when it launches short-range missiles.

Yoshihide Suga
Yoshihide Suga (Kim Kyung-Hoon/AP)

On Monday, North Korea said it had tested a new cruise missile twice over the weekend. State media described it as a “strategic weapon of great significance”, implying it was developed with the intent to carry nuclear warheads.

According to North Korean accounts, the missile demonstrated an ability to hit targets 930 miles away, putting all of Japan and US military installations there within reach.

The North Korean missile tests came as Chinese foreign minister Wang Yi was in Seoul for meetings with Mr Moon and other senior officials to discuss the stalled nuclear negotiations with the North.