North Korea vows to become a 'state nuclear force'

North Korea's state news agency has called the US-led effort to impose sanctions over its weapons programme futile, vowing the country inevitably will become a "state nuclear force".

The comments on Sunday came from the Korean Central News Agency's website Uriminzokkiri after US Secretary of State Rex Tillerson met for talks with China's top diplomats and President Xi Jinping in Beijing over the Korean nuclear crisis.

Tillerson has been a proponent of a campaign of "peaceful pressure", using US and UN sanctions and working with China to turn the screw on the regime.

But his efforts have been overshadowed by an extraordinary war of words, with US President Donald Trump mocking North Korean leader Kim Jong-un as "little rocket man" and Kim branding Trump a "dotard".