BEIJING — Secretary of State Mike Pompeo told Asian powers on Thursday that President Trump was sticking to demands that North Korea surrender its nuclear weapons, as he sought to hold together a fragile consensus on maintaining tough sanctions against the North despite Mr. Trump’s declaration that it was “no longer a nuclear threat.”

At a news conference in Seoul, South Korea, Mr. Pompeo softened some of the president’s recent comments — but did not retract them — and insisted that United Nations sanctions would remain in place until North Korea had accomplished “complete denuclearization.”

“We are going to get the complete denuclearization,” Mr. Pompeo told reporters. “Only then will there be relief from sanctions.”

He made the same point later Thursday in Beijing, where he met with China’s president, Xi Jinping. But China had already shown signs of breaking ranks on tough enforcement of the sanctions against its neighbor and trading partner, saying that with North Korea now at the negotiating table, they could legitimately be eased.