– The U.S. would be ready to talk with North Korea if it renounced further nuclear or missile tests and followed through on the pledge, U.S. Ambassador to China Terry Branstad said.

“If they announce that they’re not going to be doing any more nuclear tests and they’re not going to be launching any more missiles,” Branstad said Wednesday when asked what it would take for talks to start. “If they announce that and do that, I think there’s an opportunity for us to get back to the bargaining table.”

Branstad, speaking on the sidelines of the Fortune Global Forum in Guangzhou, also said that sanctions against North Korea were “starting to have an impact.” Calling Kim Jong Un’s push for nuclear weapons “the biggest threat to humankind right now,” Branstad repeated the Trump administration’s call for China to cut off oil sales to Kim’s regime.

“We believe we need to go further,” Branstad said. “We think oil and also these North Korean workers working in China and other countries, that needs to stop.”

President Donald Trump has sought to pressure China to rein in its ally and neighbor, which last week tested a new type of intercontinental ballistic missile. Kim said the test showed that North Korea’s nuclear program was complete because it could deliver a warhead anywhere in the U.S.

While Kim hasn’t yet proven he has the technology to put a warhead on an ICBM and deliver it safely to a target, the test has put new pressure on the U.S. and its allies to find a solution. By declaring his weapons program complete, Kim may have created a path to resume negotiations from a position of strength.

“I interpret this as a starting gun, signaling that he’s opening up the negotiating pas de deux, the dance,” Daniel Russel, former assistant U.S. secretary of state for East Asian and Pacific affairs, said after the test. “The likeliest scenario is that we’ll start seeing some initiatives from one quarter or another and there will be some testing of the ground for negotiations.”

The United Nations’ top official for political affairs is in Pyongyang this week to discuss the nuclear issue, and countries from Canada to Germany are seeking to help facilitate talks. Branstad said Canadian Prime Minister Justin Trudeau will meet with U.S. Secretary of State Rex Tillerson to discuss North Korea on Dec. 19.