Iran's nuclear envoy in the Geneva talks with Western powers has hinted there could be more rounds of meetings if the two sides fail to strike an agreement by the end of the day.

Speaking to Iranian state television from Switzerland, Abbas Araghchi says he hopes "there could be more talks in the future" if the discussions are not finalized on Friday.

He says there are "three unresolved points" but didn't elaborate.

The TV says the differences are over Iran's demands that economic sanctions against Tehran be "simultaneously reduced" as Iran carries out its obligations under a key November deal.

The ongoing Geneva talks are mapping out the implementation of that deal, which caps Iran's uranium enrichment program in return for an easing of some international sanctions for six months.