Iran's foreign minister is joining U.S. Secretary of State John Kerry for nuclear talks later this week as the clock ticks down to a June 30 deadline for a deal.

Iran's ISNA news agency said Thursday that Mohammad Javad Zarif will fly to Vienna on Friday for the talks. That's the day Kerry departs Washington for Vienna.

Foreign ministers from the five other nations at the negotiating table — Russia, China, Britain, France and Germany — are also expected to join in as they try to bridge differences between the sides on the limits Tehran must accept on its nuclear program in exchange for the lifting of economic sanctions.

But with Iran apparently backtracking on key points of the emerging deal, the talks could go past the target date.