Pyongyang, North Korea - Kim Jong Un said North Korea deployed "special assets" in response to what he called Washington's arms buildup in the South, state media reported Sunday.
The US stations about 28,500 troops in the South and last month conducted a joint military exercise with its allies South Korea and Japan.
Pyongyang routinely denounces such drills as rehearsals for invasion, while the allies insist they are defensive in nature.
"The US-ROK nuclear alliance is making rapid progress, and they are conducting various kinds of exercises to execute dangerous scenarios," Kim said in a speech marking the opening of a weapons exhibition in Pyongyang on Saturday, carried by the official Korean Central News Agency (KCNA).
"In direct proportion to the US military's arms buildup in the ROK region, our strategic concern about this region has also grown, and accordingly we have assigned our special assets to the major targets," he said, adding he was "closely watching" the military development across the border.
"The enemy... will have to worry about which direction their security environment is moving in," he added without clarifying what the special assets were.
Photos released by KCNA show Kim walking past weapons, including a missile, surrounded by North Korean generals in an indoor exhibition center.
Kim Jong Un open to talks with US
Kim last month said he was open to talks with the US, noting he had "fond memories" of President Donald Trump, on the condition that his country does not give up its nuclear arsenal.
Kim met Trump three times for high-profile summits during Trump's first term, before talks collapsed in Hanoi in 2019 over what concessions Pyongyang was prepared to make on its atomic weapons.
The US demand that Kim give up his banned weapons has long been a sticking point between the two countries, with Pyongyang under successive rounds of UN sanctions over its nuclear and missile programs.
Since the failed 2019 summit, North Korea has repeatedly said it will never give up its atomic weapons and declared itself an "irreversible" nuclear state.