Rasa News Agency reports - "This round of talks will be more serious than previous ones," Zarif said in remarks reported by the official IRNA news agency.
But we do not expect an agreement (in this round), as it is not expected in the timetable we have agreed," he added.
Iranian negotiators and representatives of the so-called P5+1 group of world powers resume talks in Vienna on Tuesday for the second time since November, seeking to transform an interim deal into a long-lasting agreement by July 20.
According to Iranian media, the latest talks will wrap up on Wednesday, a day before Iran celebrates the Persian New Year.
Under November's interim deal, Tehran froze certain nuclear activities for six months in exchange for relief from punishing sanctions hitting its economy.