North Korea conducted a simulated tactical nuclear attack drill that included two long-range cruise missiles in an exercise to “warn enemies” that the country would be prepared in case of nuclear war, the KCNA state news agency said on Sunday.

KCNA said the drill was successfully carried out on Saturday and two cruise missiles carrying mock nuclear warheads were fired towards the West Sea of the Korean peninsula and flew 1,500 kilometres at a preset altitude of 150 metres.

Pyongyang also said it would bolster its military deterrence against the United States and South Korea.

South Korea’s military said the claim of success could be an exaggeration as “not all of them succeeded”, Seoul’s Yonhap News reported, citing a senior official at the Joint Chiefs of Staff.

KCNA also reported that North Korean leader Kim Jong Un visited the Pukjung Machine Complex, which produces marine engines, and a munitions factory to stress the importance of strengthening Pyongyang’s naval forces.

“He affirmed that a future plenary meeting of the Central Committee of the WPK (Worker’s Party of Korea) would set forth an important modernisation of the complex and the development direction of the shipbuilding industry,” a KCNA statement said.

It did not specify the date of his visit.

The latest missile test came just after the joint annual exercises between South Korea and the United States, known as Ulchi Freedom Shield, came to a close on Thursday. It featured air drills with B-1B bombers.

North Korea has been stepping up its military deterrence against Washington and Seoul and has criticised last month’s summit agreement between the two on improving military cooperation.

KCNA said on August 21 that Kim recently visited a navy fleet stationed on the east coast to oversee a test of strategic cruise missiles aboard a warship and he stressed the ship would maintain striking power for combat situations.