"A good deal is possible because of significant progress in the talks, largely due to Iranian initiatives", Shamkhani wrote on his Twitter account on Thursday.
"But the final stage of the #ViennaTalks will not take place without Western political decision-making to resolve crucial issues that are required to balance the deal", he added.
Meantime, Iran's top nuclear negotiator in Vienna talks Ali Bagheri Kani said on Thursday "being near the finish line is no guarantee to crossing that".
"Being near the finish line is no guarantee to crossing that. It requires extra caution, much perseverance, additional creativity and balanced approach to take the last step," Bagheri Kani wrote on his Twitter account on Thursday.
"To finish the job, there are certain decisions that our Western interlocutors need to take," he added.
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