Iran and the U.S. are sending their top nuclear officials to Geneva, in a move that may help resolve disputes standing in the way of a deal focused on capping Tehran's atomic activities in exchange for sanctions relief.

Technical experts for both Iran and the six nations have been negotiating alongside senior political officials over the past few years. But Iranian Atomic Energy chief Ali Akbar Salehi and U.S. Energy Secretary Ernest Moniz will join in for the first time this weekend.

Western officials cautioned against undue optimism, saying the U.S. decided to send Moniz only after Iran announced that Salehi will be coming. Still, their presence could help fast-track the complex technical details of what Iran must do to secure a gradual end to economic and political sanctions.