Officials from the United States, China, Russia, Britain, France and Germany will meet on Saturday to hear Iran's response to an offer that it halt nuclear work in exchange for financial and diplomatic incentives.
The United States said on Wednesday that Deputy Secretary of State William Burns will join the talks in Geneva, stepping back from its stance of avoiding direct talks until Iran makes concessions.
Chinese Foreign Ministry spokesman Liu Jianchao said his government welcomed the U.S. step and wanted to see more give-and take from all sides.
"We welcome the United States' decision," Liu told a regular news conference, repeating China's frequent call for a negotiated solution to the dispute. He also appeared to nudge Iran to show goodwill.
"We also hope that all sides will grasp the current favourable opportunities and step up their efforts, and in particular demonstrate flexibility to advance dialogue and negotiations as early as possible."
China will be represented at the talks by Assistant Foreign Minister Liu Jieyi, spokesman Liu Jianchao said.
Iran says its uranium enrichment programme is for peaceful power generation and has repeatedly refused to stop the programme, as the six powers say it must before formal talks can begin on the package of economic and other benefits.
Tension rose further last week after Iran test-fired missiles in the Gulf, including one it says could reach Israel.
As a big oil customer of Iran and veto-wielding permanent member of the U.N. Security Council, China has become a focus of diplomatic efforts to overcome this standoff. But Beijing has been reluctant to consider steps that would threaten its energy and economic ties with Tehran. (Reporting by Chris Buckley; Editing by Ken Wills) (chris.buckley@reuters.com; +86 10 66271261)