China's UN ambassador Zhang Yesui said Tuesday it is too early to contemplate new sanctions against Iran over its refusal to halt sensitive nuclear fuel work, and called for more diplomacy.

His comments came after the United States on Monday said "the door is still open" for Iran to meet world demands on its nuclear aims, but warned it was discussing with its allies the "next steps," which could include sanctions.

China and Russia have been more reluctant to impose sanctions on Iran than the other UN Security Council members -- the United States, Britain and France -- or Germany, which works with the five to try to curb Iran's ambitions.

"This is not the right moment for sanctions," said Zhang, who chairs the UN Security Council this month.

He told reporters here that current diplomatic efforts to find a peaceful settlement "still need some more time and patience," echoing a view expressed by the Chinese foreign ministry in Beijing.

Zhang said sanctions themselves "are not an end" and a diplomatic solution "would be the best option."

In Beijing, meanwhile, foreign ministry spokesman Jiang Yu told reporters: "We believe that dialogue and negotiation are the proper way to resolve the Iran nuclear issue."

"We still have room for diplomatic efforts and we hope all parties will adopt more flexible and pragmatic policies to enhance the diplomatic efforts so as to promote an early resumption of talks," he added.

Tehran dismissed a US-set deadline of December 31 to agree to a UN-brokered nuclear fuel swap deal and instead issued the West a one-month "ultimatum" expiring January 31 to accept a counter-proposal.

The deal involves a US-backed International Atomic Energy Agency (IAEA) proposal to ship abroad low-grade nuclear fuel so it can be further enriched and returned to refuel a Tehran medical research reactor.

Such a move would offer breathing room as the big powers try to halt Iran's uranium enrichment -- which the West fears masks a drive to build a nuclear bomb. Denying the charge, Iran says it seeks peaceful uses of nuclear energy.

In Washington, State Department spokesman PJ Crowley suggested the United States still hoped China would change its position.

"It's no secret that China and the United States look at the utility of sanctions differently," Crowley told reporters when asked for comment on the Chinese remarks.

"Nonetheless, we will continue to work on this," he said, referring to an "ongoing process" of dialogue.

"At any particular time a country might say this is a good idea, this is a bad idea. We are going to continue our discussions, and we would expect to move forward with this in the coming weeks," he said.