SEOUL, South Korea (AP) — North Korea’s military said Monday its recent barrage of missile tests were practices to “mercilessly” strike key South Korean and US targets such as air bases and operation command systems with a variety of missiles that likely included nuclear-capable weapons.

The North’s announcement underscored 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 Kim also used their drills as an excuse to modernise his nuclear arsenal and increase his leverage in future dealings with Washington and Seoul.

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 of massive US-South Korean air force drills that the North views as an invasion rehearsal.

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

“The recent corresponding military operations by the Korean People’s Army 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,” the General Staff of North Korea’s military said in a statement carried by state media.

It said the weapons tests involved ballistic missiles loaded with dispersion warheads and underground infiltration warheads meant to launch strikes on enemy air bases; ground-to-air missiles designed to “annihilate” enemy aircraft at different altitudes and distances; and strategic cruise missiles that fell in international waters about 80 kilometers (50 miles) off South Korea’s southeastern costal city of Ulsan.

The North’s military said it also carried out an important test of a ballistic missile with a special functional warhead missioned with “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.

The North’s military statement did not explicitly mention a reported launch Thursday of an intercontinental ballistic missile aimed at hitting the US mainland, though its main newspaper published a photo of an ICBM-like weapon as one that was used 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.