North Korean leader Kim Jong-Un hailed a submarine-launched ballistic missile (SLBM) test as an "eye-opening success", state media said Sunday, declaring Pyongyang has the ability to strike Seoul and the US whenever it pleases.

North Korean leader Kim Jong-Un hailed a submarine-launched ballistic missile (SLBM) test as an "eye-opening success", state media said Sunday, declaring Pyongyang has the ability to strike Seoul and the US whenever it pleases.

The North's state-run KCNA news agency said the test, personally monitored by Kim, confirmed the reliability of the country's underwater launching system.

It also cited the young leader as saying Pyongyang was now capable of "hitting the heads of the South Korean puppet forces and the US imperialists anytime as it pleases."

Still images broadcast on state television showed Kim on the deck of the submarine before watching the test through binoculars from shore and meeting the crew and scientists afterwards.

"This eye-opening success constitutes one more precious gift the defence scientists and technicians are presenting to the great leaders and the party," KCNA quoted Kim as saying.

Saturday's launch came amid growing concern that Pyongyang is preparing a fifth nuclear test.

But it was followed just hours later by a North Korean offer to impose a unilateral moratorium on nuclear testing if the United States suspends annual military drills with South Korea.

The US and Britain denounced the SLBM test as a violation of UN Security Council resolutions and called on the North to refrain from further moves that could destabilise the region.

South Korea's defence ministry said the missile, fired from a submarine in the Sea of Japan (East Sea), flew around 30 kilometres (18 miles) and that the test showed "certain technological progress" in the North's SLBM capability.

"It is believed... that the North would be able to deploy the SLBM weapon within three to four years, or even sooner if it dedicates all its resources on the project," ministry spokesman Moon Sang-Gyun told reporters.