South Korean President Lee Jae Myung said he asked Chinese President Xi Jinping to serve as a mediator to help resolve the North Korean nuclear crisis and ease animosities between the two Koreas.

Lee made the request when he met Xi for a summit in Beijing on Monday, and said Xi replied that patience was needed on North Korea issues. Speaking with reporters traveling with him on the Shanghai leg of his China trip on Wednesday, Lee said China should help because channels with North Korea are effectively blocked.

“We’re making efforts but all our channels (with North Korea) are completely blocked so we can’t communicate at all. I told him it would be good for China to play the role of a mediator for peace,” Lee said in televised comments. “President Xi appraised our efforts and said we need to be patient.”

Lee added that Chinese Premier Li Qiang told him during their separate meeting Tuesday about the need to have patience as well. Lee said he told Chinese officials that neighbor states have necessary roles and that South Korea requested China to play that role, adding that China told him it would make such efforts.

Lee said he also discussed with Chinese officials South Korea’s stated push for phased, gradual denuclearization steps by North Korea in return for corresponding benefits. He said he told China it is important to freeze North Korea’s nuclear and missile programs first to prevent further expansion of North Korea’s arsenal and a potential proliferation of nuclear weapons, and that China shared that view.

“Leaving the current status would be a loss for Northeast Asia and the entire world, because (North Korea’s) nuclear weapons are being produced continuously,” Lee said.

China is North Korea’s biggest trading partner and a major diplomatic backer. South Korea and the U.S. have repeatedly asked China to use its influence to persuade North Korea to resume long-dormant diplomacy or denuclearize, while China has urged all parties involved in North Korean issues to exercise restraint.

In recent years, China has repeatedly blocked attempts by the U.S. and others to toughen sanctions on North Korea despite the country’s weapons tests being banned under U.N. resolutions. North Korea has refused to engage in dialogue with South Korea and the U.S., and has taken steps to expand its nuclear arsenal since Kim Jong Un’s high-stakes nuclear diplomacy with President Donald Trump collapsed in 2019.

Since taking office last June, Lee’s liberal government has been pushing to reopen talks with North Korea, but Pyongyang has largely ignored Lee’s overture. In July, Kim Yo Jong said the Lee government’s “blind trust” in South Korea’s alliance with the U.S. and hostility toward North Korea made it no different from its conservative predecessor.

North Korea has said it won’t put denuclearization on the negotiating table again, and many experts worry that rewarding North Korea for limited denuclearization steps could allow it to pull out of diplomacy while retaining much of its nuclear program after it wins some level of badly needed sanctions relief.