World powers resumed talks with Iran in the Kazakh city of Almaty on Friday, aiming to resolve a decade-long dispute over an Iranian nuclear programme the West suspects aims to give Tehran the capability to build an atom bomb.
In what is the second such meeting this year, the six powers - the United States, Russia, China, France, Britain and Germany - hope Iran will accept their offer of modest relief from economic sanctions in return for curbs in its most sensitive nuclear work.
"The plenary session just began this morning," a Western official said.
For years, Iran has refused to meet international demands for it to stop enriching uranium, arguing it does so only for peaceful purposes such as medical research and generation of energy.
The Almaty meeting is expected to last until Saturday and diplomats say any breakthrough is unlikely.