The United States will not agree to a phased approach to North Korea’s denuclearization, the top U.S. envoy to Pyongyang said Monday.

“We are not going to do denuclearization incrementally,” Steve Biegun told a nuclear policy conference in Washington. “The president has been clear on that and that is a position around which the U.S. government has complete unity.”

The comments suggest that the U.S. will not back down on its demand that North Korea completely give up its nuclear weapons before Washington starts relaxing sanctions on Pyongyang.

North Korea and the U.S. have publicly hardened their positions following a meeting in Hanoi, Vietnam between President Donald Trump and North Korean leader Kim Jong Un that failed to result in a deal.

U.S. officials have since threatened to expand sanctions on North Korea, while commercial satellite images suggest Pyongyang is preparing another missile test or satellite launch.