The United States is communicating with North Korea as it seeks to encourage the regime to abandon its build up of nuclear weapons, Secretary of State Rex Tillerson said.

Mr Tillerson made his comments in Beijing after holding talks with Chinese leaders on Saturday amid rising concerns over Pyongyang's military programme.

Washington is known to have back channels which it uses to help negotiate the release of US citizens who have been held captive in the North.

But Mr Tillerson's disclosure suggests US officials are also using secret talks to convince Pyongyang to hold official negotiations aimed at easing tensions.