North Korean leader Kim Jong Un said his country needed to rapidly expand its nuclear armament and called US-South Korea military exercises an “obvious expression of their will to provoke war,” state media KCNA reported on Tuesday.

South Korea and its ally the United States kicked off joint military drills this week, including testing an upgraded response to heightened North Korean nuclear threats.

Pyongyang regularly criticises such drills as rehearsals for invasion and sometimes responds with weapons tests, but Seoul and Washington say they are purely defensive.

The 11-day annual exercises, called Ulchi Freedom Shield, will be on a similar scale to 2024 but adjusted by rescheduling 20 out of 40 field training events to September, South Korea’s military said earlier. Those delays come as South Korean President Lee Jae Myung says he wants to ease tensions with North Korea, though analysts are sceptical about Pyongyang’s response.

The exercises were a “clear expression of ... their intention to remain most hostile and confrontational” to North Korea, Kim said during his visit to a navy destroyer on Monday, according to KCNA’s English translation of his remarks.

He said the security environment required the North to “rapidly expand” its nuclear armament, noting that recent US-South Korea exercises involved a “nuclear element”.

Efforts by the United States and its allies to tackle North Korea’s development of nuclear weapons are expected to be discussed at an upcoming meeting between US President Donald Trump and South Korean President Lee Jae Myung in Washington.

“Through this move, North Korea is demonstrating its refusal to accept denuclearisation and the will to irreversibly upgrade nuclear weapons,” said Hong Min, North Korea analyst at the Korea Institute for National Unification.

A report by the Federation of American Scientists last year concluded that while North Korea may have produced enough fissile material to build up to 90 nuclear warheads, it had likely assembled closer to 50.

North Korea plans to build a third 5,000-tonne Choe Hyon-class destroyer by October next year and is testing cruise and anti-air missiles for those warships.