North Korean leader Kim Jong-un says his country has developed the capability to hit all of US mainland with its nuclear weapons, and that the "nuclear launch button" is on his desk.

During a televised New Year’s day speech on Monday, Kim said,"These weapons will be used only if our security is threatened."

"The entire United States is within range of our nuclear weapons, and a nuclear button is always on my desk. This is reality, not a threat," he added.

"This year we should focus on mass producing nuclear warheads and ballistic missiles for operational deployment," he added.

Kim also stressed that it is extremely important that military tensions on the Korean peninsula be lowered, while adding that the path to dialogue with South Korea was open.

A man watches a television news broadcast showing North Korean leader Kim Jong-un's New Year's speech, at a railway station in Seoul on January 1, 2018.

He added that Pyongyang was mulling the sending of a delegation to the Winter Olympics Games which are set to be held at Pyeongchang, South Korea, in February.

"North Korea's participation in the Winter Games will be a good opportunity to show unity of the people and we wish the Games will be a success. Officials from the two Koreas may urgently meet to discuss the possibility," Kim added.

North Korea has been under a raft of harsh UN sanctions since 2006 over its nuclear tests as well as multiple rocket and missile launches. Pyongyang has firmly defended its military program as a deterrent against the hostile policies of the US and its regional allies, including South Korea and Japan.

On November 29, North Korea said it had successfully tested a new missile that put the US mainland within range of its nuclear weapons. It also declared itself a “nuclear state.”