“Let me be very clear: the policy of strategic patience has ended. We are exploring a new range of security and diplomatic measures. All options are on the table,” Tillerson told a news conference in Seoul.

He said any North Korean actions that threatened the South would be met with “an appropriate response”.

“If they elevate the threat of their weapons programme to a level that we believe requires action, that option is on the table,” Tillerson said when asked about military action.

Tillerson also called on China to implement sanctions against North Korea, and said there was no need for China to punish South Korea for deploying an advanced US anti-missile system aimed at defending against North Korea.