North Korean leader Kim Jong-un has called for bolstering the country's nuclear forces "without limitation" and completing war preparations as the country's enemies have increased "frantic" military confrontations with North Korea, state media reported Monday.

Kim made the remark during the 4th Conference of Battalion Commanders and Political Instructors of the Korean People's Army on Friday, the final day of the two-day event held in Pyongyang, according to the Korean Central News Agency. It marked the first such conference in 10 years.

The North's leader called for military officials to focus on completing war preparations, stressing that North Korea should continue to bolster its nuclear forces to accomplish a mission to deter war.

"We will strengthen our self-defense power, centered on nuclear forces, without limitation, not being content (with our current level) and ceaselessly," Kim said at his speech.

He also called trilateral cooperation by South Korea, the United States and Japan a "critical" factor that threatens peace and stability on the Korean Peninsula.

"US-led military alliance has been expanding into more larger areas encompassing Europe and the Asia-Pacific region," Kim said.

The North's leader claimed the US and the West have been staging a war against Russia using Ukraine as "shock troops" in a bid to expand the scope of Washington's military intervention into the world, according to the KCNA.

But Kim did not mention North Korea's deployment of troops to Russia to support Moscow's war with Ukraine.

Kim's speech came as the leaders of South Korea, the US and Japan held a trilateral summit on the sidelines of the Asia-Pacific Economic Cooperation summit in Peru on Friday and condemned North Korea's deepening military cooperation with Russia.

South Korea and the US have confirmed that North Korean soldiers have engaged in combat operations against Ukrainian forces in Russia's western Kursk border region. (Yonhap)