Kim Jong Un has ordered his country's military, munitions industry and nuclear weapons sector to accelerate war preparations.
The North Korean leader said this was due to unprecedented confrontational moves by the US, state media reported on Thursday.
Speaking on the policy directions for the new year at a key meeting of the country's ruling party on Wednesday, Kim also said Pyongyang would expand strategic cooperation with "anti-imperialist independent" countries, news agency KCNA reported.
North Korea has been growing ties with Russia, among others, as Washington accuses Pyongyang of supplying military equipment to Moscow for use in its war with Ukraine, while Russia provides technical support to help the North advance its military capabilities.
"He (Kim) set forth the militant tasks for the People's Army and the munitions industry, nuclear weapons and civil defence sectors to further accelerate the war preparations," KCNA said.
On Thursday, South Korean President Yoon Suk Yeol visited a frontline military unit in the eastern county of Yeoncheon to inspect its defence posture and called for an immediate retaliation if there was any provocation from North Korea.
"I urge you to immediately and firmly crush the enemy's will for a provocation on the spot," he told troops.
During the party plenum, North Korea's Kim also laid out economic goals for the new year, calling it a "decisive year" to accomplish the country's five-year development plan, KCNA said.
"He clarified the important tasks for the new year to be dynamically pushed forward in the key industrial sectors," and called for "stabilising the agricultural production on a high level."
The North has suffered serious food shortages in recent decades, including famine in the 1990s, often as a result of natural disasters. International experts have warned that border closures during the COVID-19 pandemic worsened food security.
North Korea's crop output was estimated to have increased year-on-year in 2023 due to favourable weather conditions. But a Seoul official has said the amount was still far below what is needed to address the country's chronic food shortages.
The 9th plenary meeting of the 8th central committee of the Workers' Party of Korea kicked off on Tuesday to wrap up a year during which the isolated North enshrined nuclear policy in its constitution, launched a spy satellite and fired a new intercontinental ballistic missile.
The days-long assembly of the party and government officials has been used in recent years to make key policy announcements. Previously, state media released Kim's speech on New Year's Day.
