UNITED NATIONS — China pledged for the first time Wednesday to join in substantive talks on sanctioning Iran for defying U.N. demands that it stop enriching uranium, according to Britain’s U.N. ambassador.

Liu Zhenmin, China’s newly appointed negotiator on the Iranian nuclear crisis, participated in a conference call on Iran’s nuclear program Wednesday morning with the political directors from the United States, Russia, France, Britain and Germany. However, China’s U.N. envoy, Li Baodong, said Beijing remains committed to resolving the nuclear standoff with Iran through negotiations.