The United States has pledged to step up its drive for new UN sanctions on Iran and warned China against blocking diplomatic efforts to halt the Islamic republic's nuclear ambitions.
US officials talked tough after the UN's International Atomic Energy Agency (IAEA) said Iran had made "substantial progress" in revealing contents of its nuclear programme, but needed to be more pro-active in providing information.
"This report sadly makes clear that Iran seems uninterested in working with the rest of the world," White House spokeswoman Dana Perino said of the widely awaited IAEA assessment yesterday.
At the United Nations, US envoy Zalmay Khalilzad accused China of blocking progress on a third round of sanctions to punish Iran's refusal to halt uranium enrichment.
Enriched uranium can be used to generate nuclear power, but also in a highly refined form, to make nuclear weapons.
"I don't think China would want to be in a position to cause a failure of diplomacy to deal with this issue," Khalilzad told reporters.
The United States has never ruled out military action if Iran persists with its atomic drive, and has stepped up its rhetoric of late to warn of "World War III" if Tehran gains the know-how to make nuclear weapons.
A senior UN official confirmed a claim by Iranian President Mahmoud Ahmadinejad that Iran had reached a key target of 3,000 centrifuges enriching uranium.
Scientists say that number could be sufficient to produce enough enriched uranium in one year to make a single nuclear bomb.