North Korea says missile tests were practice for attacks on South and US

North Korea's military has said its recent missile tests were practice to "mercilessly" strike key South Korean and US targets – such as air bases and operation command systems – with a variety of weapons likely to have included nuclear-capable ones.

The North’s announcement underlined leader Kim Jong Un's determination not to back down in the face of his rivals' push to expand their military exercises.

But some experts say he also used their drills as an excuse to modernise his nuclear arsenal and increase his leverage in future dealings with Washington and Seoul.

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North Korea fired dozens of missiles and flew warplanes toward the sea last week – triggering evacuation alerts in some South Korean and Japanese areas – in protest at massive US-South Korean air force drills that the North views as an invasion rehearsal.

US and South Korean officials responded that they would further enhance their joint training events and warned the North that the use of nuclear weapons would result in the end of Mr Kim's regime.

Watch: The threat of North Korea and their hypersonic missiles.

The General Staff of North Korea's military said in a statement carried by state media the North's operations "are a clear answer of (North Korea) that the more persistently the enemies' provocative military moves continue, the more thoroughly and mercilessly the KPA will counter them".

It said the weapons tests involved ballistic missiles loaded with dispersion warheads and underground infiltration warheads meant to launch strikes on enemy air bases.

It also said the tests included ground-to-air missiles designed to "annihilate" enemy aircraft at different altitudes and distances and strategic cruise missiles that fell in international waters about 50 miles (80km) off South Korea's south-eastern coastal city of Ulsan.

The North's military said it also carried out an important test of a ballistic missile with a special functional warhead aimed at "paralysing the operation command system of the enemy".

This could mean a simulation of electromagnetic pulse attacks, but some observers doubt whether North Korea has mastered key technologies to obtain such an attack capability.

Watch: Exploring North Korea's nuclear weapon capability.

The North's military statement did not explicitly mention a reported launch last Thursday of an intercontinental ballistic missile aimed at hitting the US mainland, though its main newspaper published a photo of an ICBM-like missile as one of the weapons mobilised during last week's testing activities.

Some experts say many other North Korean missiles launched last week were short-range nuclear-capable weapons that place key military targets in South Korea, including US military bases there, within striking range.

Later on Monday, South Korea's military disputed some of the North's accounts of its missile tests.

Spokesman Kim Jun-rak said South Korea did not detect the North's cruise missile launches and that it is also notable that North Korea did not mention what Seoul assessed as an abnormal flight by an ICBM.

It comes following this year's 'Vigilant Storm' air force drills between the United States and South Korea – the largest-ever for the annual autumn manoeuvres.

They involved 240 warplanes including advanced F-35 fighter jets from both countries.