Iran's foreign ministry said there was hope for a step forward, as negotiations on the country's nuclear programme were due to start in Geneva on Tuesday (October 15).
The talks will be the first since the election of President Hassan Rouhani, a relative moderate who wants to thaw Iran's icy relations with the West to get harsh economic sanctions removed.
Speaking on Monday (October 14) Iranian foreign ministry spokesman Hassan Ghashghavi said there was cause for optimism.
"I think there's no reason for the two sides not to be optimistic about resolving the issues. Although we know that in politics absolute optimism and absolute pessimism are both harmful, and in fact, it is the round table that will determine the direction of the future," he said.
On Sunday (October 13) Iran rejected the West's demand that it send sensitive nuclear material out of the country but signalled flexibility on other aspects of its atomic activities that worry world powers.
Six world powers - the United States, Russia, China, France, Britain and Germany - will take part in the talks that are expected to continue until Wednesday (October 16).
Western nations believe Iran's uranium enrichment programme is an attempt to achieve a nuclear weapons capability, a charge Tehran denies, saying it only wants to master the technology to generate electricity and carry out medical research.
In negotiations since early 2012, world powers have demanded that Iran suspend 20-percent enrichment, send some of its existing uranium stockpiles abroad and shutter the Fordow underground site, where most higher-grade enrichment is done.
In return, they offered to lift sanctions on trade in gold, precious metals and petrochemicals but Iran, which wants oil and banking restrictions to be removed, has dismissed that offer. It says it needs 20-percent uranium for a medical research reactor.
Presented by Adam Justice