Standing beside North Korea's largest missiles, leader Kim Jong Un said his country's weapons development is necessary in the face of hostile policies from the United States and a military buildup in South Korea, state media said on Tuesday.

Pyongyang was only increasing its military in self-defence and not to start a war, Kim told a defence exhibition on Monday, North Korea's official KCNA news agency reported.

Kim made his remarks standing next to a variety of weapons, including the country's intercontinental ballistic missiles, the ruling party newspaper Rodong Sinmun showed. Among them was the Hwasong-16, North Korea's largest ICBM, unveiled at a military parade in October 2020 but not yet test-fired.

"We are not discussing war with anyone, but rather to prevent war itself and to literally increase war deterrence for the protection of national sovereignty," Kim said.

State television footage showed a smiling Kim clapping as shirtless soldiers used their hands to smash bricks placed on colleagues' chests and others broke chains wrapped around their bodies in shows of strength.

Kim also saluted jets leaving coloured trails during an air show, while strolling through missiles on display.

South Korea's defence ministry said South Korean and US intelligence agencies were analysing the equipment displayed.

A spokesperson for the US State Department reiterated that the US goal was the complete denuclearisation of the Korean peninsula, but that Washington "harbours no hostile intent" towards North Korea and is prepared to meet with it without preconditions for "serious and sustained diplomacy".

"The United States has a vital interest in deterring the DPRK, defending against its provocations or uses of force, and in limiting the reach of its most dangerous weapons programmes, and above all keeping the American people and our allies safe," the spokesperson added, using the initials for North Korea's official name, the Democratic People's Republic of Korea.

Pyongyang has said it is not interested in talks as long as Washington maintains policies such as sanctions and military activities in South Korea.

Washington's assertions that it holds no hostile feelings toward North Korea were hard to believe in the face of its continued "wrong judgements and actions", Kim said.

The two Koreas have been in an accelerating arms race, with both sides testing increasingly advanced short-range ballistic missiles and other hardware.

South Korea recently test fired its first submarine-launched ballistic missile, plans to build aircraft carriers and has bought American-made F-35 stealth fighters.

North Korea has pushed ahead with its missile programme, and analysts say it has begun a major expansion of its main nuclear reactor, used to produce fuel for nuclear bombs.

South Korea's national security adviser, Suh Hoon, met his American counterpart, Jake Sullivan, in Washington recently to discuss North Korea.

Suh told reporters he planned to discuss South Korean President Moon Jae-in's proposal for a formal end to the 1950-1953 Korean War and for possible easing of sanctions on North Korea.

A White House statement on the meeting said Sullivan stressed the need for North Korea "to refrain from escalatory actions" and reaffirmed support for inter-Korean dialogue and cooperation.

A senior official of the US administration said Washington had made specific proposals for discussions to North Korea but had not received a response from Pyongyang. "We remain prepared to meet to discuss the full range of issues," he said.

Last week the two Koreas restored their hotlines that North Korea severed months ago, with Pyongyang urging Seoul to step up efforts to improve relations after criticising what it called double standards over weapons development.

Kim said Seoul's "unrestricted and dangerous" efforts to strengthen its military were "destroying the military balance in the Korean peninsula and increasing military instability and danger".

"Under the absurd pretext of suppressing our threats, South Korea has openly expressed its desire to gain an edge over us in military power on various occasions," he added.