North Korea's nuclear weapons status is irreversible, and the more the US and its allies advocate denuclearisation, the more the country's stance will harden, state news agency KCNA cited North Korea's Foreign Minister Choe Son Hui as saying on Thursday.

Choe was responding to a meeting between the United States, South Korea and Japan this week, where they reaffirmed their commitment to the complete denuclearisation of North Korea.

Also on Thursday, KCNA reported that North Korea had conducted a test firing of an upgraded 240mm guided multiple rocket launcher system on Tuesday, saying the weapon would bolster firepower along the country's southern border.