Rex Tillerson has said that the US is ready to begin exploratory talks with North Korea “without preconditions”, but only after a “period of quiet” without new nuclear or missile tests.

The secretary of state’s remarks appeared to mark a shift in state department policy, which had previously required Pyongyang to show it was “serious” about giving up its nuclear arsenal before contacts could start. And the language was a long way from repeated comments by Donald Trump that such contacts are a “waste of time”.

Tillerson also revealed that the US had been talking to China about what each country would do in the event of a conflict or regime collapse in North Korea, saying that the Trump administration had given Beijing assurances that US troops would pull back to the 38th parallel, which divides North and South Korea, and that the only US concern would be to secure the regime’s nuclear weapons.

Earlier this week it emerged that China is building a network of refugee camps along its 880-mile (1,416km) border with North Korea, in preparation for a potential exodus that could be unleashed by conflict or the collapse of Kim Jong-un’s regime.

Speaking at the Atlantic Council thinktank in Washington, Tillerson made it explicit that the message to Pyongyang had changed and that the North Korean regime did not have to commit to full disarmament before direct diplomacy could take off.

“We are ready to talk anytime North Korea would like to talk. We are ready to have the first meeting without preconditions. Let’s just meet,” Tillerson said. “And then we can begin to lay out a roadmap … It’s not realistic to say we are only going to talk if you come to the table ready to give up your program. They have too much invested in it.