Iran's foreign minister says his country and six others have made "significant progress" at marathon all-night nuclear talk sessions meant to reach a preliminary understanding on the curbs Tehran must accept on atomic activities in exchange for a lifting of sanctions.

But Mohammad Javad Zarif said Thursday that agreement still remains to be written, adding there is not yet a "final result."

Asked if that would be possible during the day, Iranian nuclear chief Ali Akbar Salehi said "the sunrise is just ahead."

The negotiators want to issue a joint statement outlining general political commitments to resolve concerns about Iran's nuclear program, and the pace of lifting sanctions. They are also trying to fashion more detailed documents on the steps they must take by June 30 to meet those goals.