SEOUL: North Korea's foreign ministry denounced a US planned sale of Apache helicopters to South Korea, state media KCNA said on Friday, vowing to take additional steps to bolster its self-defence.

The Pentagon said on Monday that the US State Department has approved the potential sale of Apache helicopters and related logistics and support to South Korea for an estimated $3.5 billion.

An unnamed senior official in charge of foreign news at North Korea's foreign ministry issued a press statement on Thursday criticising the sale plan as a move to aggravate tension, alongside ongoing annual military drills by the allies.

"This is a reckless provocative act of deliberately increasing the security instability in the region," the official said, according to KCNA.

The official accused Washington of escalating military confrontation, "disturbing the military balance and thus increasing the danger of a new conflict" in the region by supplying lethal weapons to its allies and friends.

Pyongyang's "strategic deterrence will be further strengthened to protect the national security and interests and the regional peace," the statement said, pledging to steadily conduct military activities to boost self-defence.