The drill was conducted to review the artillery units' capacity to handle nuclear warheads and stage military operations in a swift manner, the KCNA said.

The launch of the missiles that flew about 1,000 kilometers was seen as a response to the ongoing joint military exercise between Seoul and Washington, which North Korea denounces as a war rehearsal against the North. Three out of the missiles landed in Japan's exclusive economic zone.

The KCNA said Kim ordered the units to be fully ready to open fire to annihilate the enemies once the ruling Workers' Party of Korea gives the order.

The North's leader ordered the force to "keep highly alert as demanded by the grim situation in which an actual war may break out anytime," it said.

He gave officials tasks to "continuously develop Korean-style ultra-precision and intellectually promoted rockets and bolster them in quality and quantity," the KCNA said, adding that artillerymen should carry out their duty as a "credible nuclear force" of the party.

One day after the North's provocation, Seoul and Washington began the deployment of an advanced US missile system on South Korean soil with the first elements of the THAAD system arriving here a day earlier.

The latest test came amid intensified pressure against North Korea following its provocation in February and the killing of the half brother of the country's leader in Malaysia.

Pyongyang test-fired a new intermediate ballistic missile on Feb. 12, the first missile launch since US President Donald Trump took office in January.

The South Korean military said that the missile appeared to be developed with technology from submarine-launched ballistic missiles.

North Korea is banned from testing any ballistic missile technology under a set of UN resolutions. Pyongyang carried out two nuclear tests last year alone and launched ballistic missiles in defiance of international condemnation.

Talk of Washington's move to reintroduce tactical US nuclear weapons to South Korea has resurfaced after the New York Times reported over the weekend that Trump is looking into that possibility as a "dramatic warning" to Pyongyang as it crafted its North Korea policy.

Analyzing photos released by North Korea, experts said that the North seemed to test-fire four Scud-ER missiles, an upgraded version of a short-range Scud-C missile.

Analysts said that North Korea seemed to show that it has an ability to make standardized nuclear weapons by highlighting the artillery units' capacity to handle nuclear warheads.

"Pyongyang appeared to have ratcheted up its threat from the perspective of missile operations," said Kim Dong-yub, a professor at the Institute for Far Eastern Studies in Kyungnam University.

The KCNA said that the leader's entourage included Gen. Kim Rak-gyom, commander of the Strategic Force, who returned to the public eye after a six-month hiatus.

Kim, the missile operation commander, had disappeared from public view after he watched the military's fire drill for ballistic rockets in September last year.

His absence from major military events had spawned speculation he might have been punished for a series of failed test launches of intermediate-range Musudan missiles last year. (Yonhap)