SEOUL, South Korea (AP) — North Korean authorities have detained four officials over the recent failed launch of a naval destroyer, an incident that leader Kim Jong Un said was caused by criminal negligence, state media said.

It’s rare for North Korea to publicly impose severe punishments against officials over botched weapons tests or military displays. The weekend arrests of the four officials signal how serious Kim is about his military build-up plan and bolstering discipline at home.

The 5,000-ton-class destroyer was damaged Wednesday in the presence of Kim when a transport cradle on the ship’s stern detached early during a launch ceremony at the northeastern port of Chongjin. Satellite imagery on the site showed the vessel lying on its side and draped in blue covers, with parts of the ship submerged.

The incident infuriated Kim as the warship — the country’s second known destroyer — is key to his naval forces modernization plan. Kim quickly blamed military officials, scientists and shipyard operators for what he called a “criminal act caused by absolute carelessness, irresponsibility and unscientific empiricism.”

The official Korean Central News Agency said Monday that law enforcement authorities detained Ri Hyong Son, vice director of the munitions industry department at the ruling Workers Party’s Central Committee, who said it was “greatly responsible” for the failed launch.

KCNA reported Sunday that the authorities detained three officials at Chongjin Shipyard over the incident — the chief engineer, head of the hull construction workshop and deputy manager for administrative affairs.

Hong Kil Ho, the shipyard manager, also was summoned for questioning, KCNA previously reported.

In an instruction to investigators Thursday, North Korea’s powerful Central Miliary Commission said those responsible “can never evade their responsibility for the crime.” But it’s unclear what punishment the arrested officials would receive.

Earlier in his rule, Kim gained notoriety for engineering a spate of executions and purges of senior officials, including the killing of his powerful uncle. But observers say those actions were largely meant to solidify his grip on power and eliminate potential threats to his rule. In recent years, there have been few reports of executions or purges in North Korea as Kim has built up the absolute power similar to that of his late father and grandfather.

Kim has reportedly granted preferential treatments to scientists and engineers involved in the weapons development industry as he has pushed hard to expand his nuclear and missile arsenals. Kim has allocated new apartments in Pyongyang to them, and after a failed launch of a military spy satellite last year, he issued a supportive message toward his scientists over the setback, saying “a failure is always a prerequisite for success,” according to state media.

Experts say Kim is eager to achieve major progress in his five-year arms development plan set during a ruling party congress in early 2021. Kim has said North Korea needs greater naval forces as well as nuclear-capable missiles and other sophisticated weapons to cope with what he calls escalating U.S.-led security threats.

Last month, North Korea launched its first destroyer, also a 5,000-ton-class ship, with massive fanfare. The ship is North Korea’s largest and most advanced warship and state media reported it is designed to carry various weapons including nuclear missiles. Kim called its construction “a breakthrough” in modernizing North Korea’s naval forces.

North Korea denied the second destroyer suffered major damage, saying the hull on the starboard side was scratched and some seawater flowed into the stern section.

North Korea said Friday it needed about 10 days to make repairs, but many outside observers said the country likely understated the damage.

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Associated Press writer Kim Tong-hyung contributed to this report.