Talks on Iran's nuclear program have entered what participants hope is the final round. But substantial differences could mean they are extended beyond the Nov. 24 target date for a deal.

The talks group Iran around the negotiating table with the U.S., Russia, China, Britain, France and Germany. They resumed Tuesday with EU official Catherine Ashton, who coordinates the meetings, conferring with Iranian Foreign Minister Mohammad Javad Zarif. A full session is planned for later in the day.

The six want Iran to curb nuclear programs that could be used for making atomic arms. In exchange, they offer an end to sanctions on the Islamic Republic. Tehran insists it does not want such weapons and is resisting deep cuts in its program.