"Submarines rapidly submerged to make torpedo-attacks at the 'enemy' warships while fighters and bombers made zero feet flight above the sea to drop bombs on the targets," the report said.

"More than 300 large-caliber self-propelled guns lined up along the coast opened fire all at once," it added.

North Korea carried out the large-scale conventional military exercise instead of staging another nuclear test or missile provocation. North Korea has detonated five nuclear devices since 2006 and test-fired several missiles this year.

The drill is viewed as a show of force, as the US Carl Vinson aircraft carrier is heading toward the Korean Peninsula amid tensions over signs of the North's provocations.

Mobilization of self-propelled artillery pieces which can reach Seoul and its adjacent areas indicated that Pyongyang seeks to demonstrate its readiness to attack the South if Washington stages a pre-emptive strike on the North, experts say.

"North Korea appeared to show off its military capabilities by mobilizing (its assets) including fighter jets and submarines," Lee Duk-haeng, spokesman at Seoul's unification ministry, told a regular press briefing.

"To mark the anniversary, the country also seemed to aim to inspire the military's self-confidence (through the drill) internally."

The US navy strike group is expected to arrive near the peninsula this weekend for a joint training exercise with South Korean naval ships. The USS Michigan, a nuclear-powered submarine, also made a port call in South Korea on Tuesday.

The US has called on China to use its leverage over North Korea to rein in the repressive regime. US President Donald Trump on Monday dubbed North Korea a "real threat to the world," calling for tougher UN sanctions.

North Korea's media warned that its military is ready to "sink" the carrier "with a single strike" if needed.

Pyongyang held a massive military parade on April 15 to mark the 105th birthday of late state founder Kim Il-sung, the grandfather of the current leader. It displayed prototypes of three intercontinental ballistic missiles in a show of force.

"The latest fire drill is seen as part of North Korea's wrap-up of a months-long winter training program," said Kim Dong-yub, a professor at the Institute for Far Eastern Studies in Kyungnam University.

"I don't think the artillery drill was hastily arranged just to counter Washington's latest move. I think North Korea would fire a missile (to flex its military muscle)."

Meanwhile, among key officials in attendance was Kim Won-hong, a spy chief who was reportedly sacked in mid-January due to abuse of power, the country's TV broadcaster said.

Since the dismissal, Kim made his first public appearance at the recent military parade with the badge of a general on his suit in a possible sign that he may have been reinstated. Kim was demoted to major general concurrent with the dismissal.

But it was not confirmed whether Kim was reinstated as state media did not mention his title on Wednesday. (Yonhap)