Major world powers will meet in Vienna later this week to finalise a package of incentives for Iran to halt nuclear fuel enrichment along with penalties if it keeps defying international pressure.
The United States, Britain, France, China, Russia and Germany failed to resolve differences at London talks last week over the extent of sweeteners for Iran or the nature and timing of sanctions if Tehran keeps enriching uranium.
The Chinese government said the sextet's foreign ministers would convene on Thursday in Vienna, where the watchdog International Atomic Energy Agency is based.
British and European Union officials also confirmed the meeting.
EU foreign policy chief Javier Solana indicated on Sunday some differences remained but that the six powers were "getting very close" to consensus after further consultations.
Tehran says it seeks nuclear energy only for electricity. Western powers suspect Iran's programme is a civilian cover for efforts to master technology to build atom bombs.
Diplomats said last week the incentives prepared by Britain, France and Germany for Iran would include a light-water nuclear reactor and an assured foreign supply of fuel for civilian power plants so Iran would not have to enrich uranium at home.
But Washington has been wary about transferring reactor technology that might be diverted into secret bomb production. Sanctions could entail visa bans and a freeze on assets of senior Iranian officials before resorting to trade measures.
But Russia and China, two of the five veto-holding Security Council powers, are opposed to a Western thrust to brand Iran a "threat to international peace and security" in the proposed council resolution.
They argue this could lead to US-led military action against a state not proven to be seeking atomic bombs in secret.
Iran hid uranium-enrichment research from UN nuclear inspectors for almost 20 years, continues to deflect UN investigations and has failed in Western eyes to justify why it needs nuclear power when it is the world's fourth-largest oil producer.