DUBAI (Reuters) -Iran's chief negotiator in nuclear talks with world powers in Vienna, Ali Bagheri Kani, returned to the Austrian capital on Wednesday morning after consultations in Tehran, Iranian semi-official ISNA news agency reported on Wednesday.

       The 2015 deal that lifted sanctions on Iran in return for curbs on its nuclear programme is within touching distance of being restored after eleven months of talks.

       But the negotiations have been complicated by a last-minute demand from Russia for guarantees from the United States that Western sanctions targeting Moscow over its invasion of Ukraine would not affect its business with Iran.

       Western powers on Tuesday warned Russia against wrecking the almost completed deal on bringing the United States and Iran back into compliance with the accord.

       The talks' coordinator, Enrique Mora of the European Union, said on Monday the time had come for political decisions to be taken to end the negotiations.

       (Reporting by Dubai NewsroomEditing by Michael Georgy, Alison Williams and John Stonestreet)