The United States says China has agreed to join discussions on possible new sanctions against Iran over its nuclear programme.
US officials said on Wednesday that diplomats from the five permanent members of the UN Security Council and Germany, known as the "P5+1" group, were unified on the issue of Iran sanctions.
The Obama administration has welcomed the news, saying that China's agreement to serious negotiations with Western powers on potential new sanctions was an important step forward.
White House spokesman Bill Burton said that the international community would seek to "put pressure" on Iran this spring.
The announcement comes as Iran's chief nuclear negotiator visits China to discuss the latest developments.
China has until now been opposed to new sanctions, with senior Chinese diplomats to the UN repeatedly saying diplomacy was their preferred route.
Just this week, Qin Gang, a Chinese foreign ministry spokesman, said in Beijing that "China opposes Iran possessing nuclear weapons, but at the same time we believe that, as a sovereign state, Iran has the right to peacefully develop nuclear energy".
But US officials said Beijing indicated a shift away from its previous reluctance during a conference call among the six powers.
Speaking at the UN headquarters in New York City on Wednesday, Hillary Clinton, the US secretary of state, said the officials had "accurately described'' the group's position.
"There will be a great deal of further consultation, not only among the P5+1 but other members of the Security Council and other member nations during the next weeks," she said
Clinton said on Tuesday that Iran had repeatedly shown an unwillingness to fulfil its international obligations over the last 15 months.
"That's the basis on which I express my optimism that we're going to have a consensus reached in the security council," she said after a Group of Eight foreign ministers meeting in Canada.
"We see a growing awareness on the part of many countries - including China - as to the consequences of a nuclear-armed Iran to regional and global stability, to our oil supply, and we think that there will be a consensus reached as to the best way forward," she said.
Barack Obama, the US president, said on Tuesday that he hoped to have Iran sanctions in place within weeks.
China's support, or at least acquiescence, is crucial to fulfilling that goal as it is a permanent member of the Security Council with the power to veto any resolution.
'Long way to go'
But Al Jazeera's Cath Turner, reporting from the UN, said the major powers had only agreed to compile a list of possible sanctions to be discussed before a draft resolution is draw up and presented for vote at the security council.
"Looking very closely at what has been agreed on, there is a long way to go until China is supposed to be supporting a new draft resolution for sanctions on Iran," our correspondent said.
"We need to be very careful that we don't buy into the American language of optimism and trumpeting some kind of breakthrough when really, it's only a very small step on a very long way to sanctions against Iran."
Russia, like China, reluctantly backed three previous rounds of UN sanctions against Iran for refusing to halt uranium enrichment as demanded by five Security Council resolutions.
Iran rejects Western charges that its atomic programme is aimed at developing bombs and says enrichment is a sovereign right, insisting that its nuclear programme is peaceful and intended only to generate electricity.
Against this backdrop of diplomatic tensions, Iran's chief negotiator on nuclear matters visited China on Thursday to discuss the growing possibility of new sanctions.
Saeed Jalili was invited by Dai Bingguo, a senior Chinese diplomat who serves as a state councillor advising leaders on foreign policy, the official Xinhua news agency said.
Some analysts say China will push to ensure any possible sanctions do not threaten its energy and trade ties with Iran.
In 2009 Iran was the third-biggest foreign supplier of crude oil to China, which is the world's second-biggest consumer of oil after the US.