Iran's top nuclear official is holding talks in China amid signs that Beijing has relaxed its opposition to a new round of UN sanctions against Tehran.
The US ambassador to the UN, Susan Rice, said China was ready to hold "serious" talks with Western powers on a new UN resolution.
This would mark a policy shift for China, which has strong ties with Iran. China says it wants a peaceful outcome.
Western powers claim Iran seeks nuclear weapons, a charge Tehran denies.
China has in the past expressed reluctance to see new sanctions imposed, and as a permanent member of the UN Security Council, along with France, the US, the UK, and Russia, it has the power to veto such a move.
US President Barack Obama, meanwhile, has said he hopes to have sanctions in place "within weeks".
'Tough sanctions regime'
Beijing made the commitment to talks in a phone call on Wednesday, US officials told the Associated Press news agency.
Ms Rice said the US, the UK, France, Germany, Russia and China had agreed to begin drafting a UN resolution on Iran's nuclear programme.
She told CNN: "China has agreed to sit down and begin serious negotiations here in New York with the others in the [group of six] ... as a first step towards getting the entire Security Council on board with a tough sanctions regime against Iran.
"This is progress, but the negotiations have yet to begin in earnest."
Chinese Foreign Ministry spokesman Qin Gang said President Hu Jintao would attend a summit on nuclear security in Washington later in the month.
Mr Qin did not comment directly on Ms Rice's words but, in response to a question about them, said: "We have always and will continue to push for a peaceful settlement of this issue."
He added the standoff should be resolved by "diplomatic means".
"China strongly values the nuclear security issue and opposes nuclear proliferation and nuclear terrorism," he said.
Meanwhile Iran's chief nuclear negotiator Saeed Jalili arrived in Beijing for "bilateral talks and to discuss the nuclear issue", Iran's Irna news agency reported.
"The relationship between Iran and China is very important, and it is very important for our two countries to cooperate on all the issues," he told Iranian media.
On Wednesday, US media reported an Iranian nuclear scientist had defected.
ABC News said Shahram Amiri had been resettled in the US and was helping the CIA try to block Iran's nuclear programme.
Iran accused the US of abducting him, but Washington has denied any knowledge of the scientist.