VIENNA -- Iran's full delegation arrived in Vienna on Tuesday to complete a final, comprehensive agreement with world powers that will govern its nuclear program going forward.Tuesday was originally the self-imposed deadline for that deal, however the P5+1 group of world powers and Iran agreed to formally extend the terms of the interim agreement by seven days to buy time for a comprehensive deal.Iranian Foreign Minister Mohammad Javad Zarif was accompanied by Ali Akbar Salehi, the country's chief technical expert at the talks, as well as Iranian President Hassan Rouhani's brother and several of their aides.Zarif told Iranian press that he had been in Tehran for consultations on Monday. But arriving at the Coburg Palace here in the Austrian capital, he rejected that he had traveled back to Iran for 24 hours to receive a mandate to close the deal from Supreme Leader Ayatollah Ali Khamenei."I didn't go to get a mandate," he said. "I already had a mandate to negotiate. And I'm here to get a final deal, and I think we can."During Zarif's bilateral meeting with US Secretary of State John Kerry— which lasted an hour— Khamenei sent out a message on Twitter blessing his negotiating team."I recognize our negotiators as trustworthy, committed, brave and faithful," he said, along with a photo of the team in white lab coats and the hashtag, "#IranTalks."On Monday, a senior Obama administration official said that negotiations could go on for days, but that this was the final round— and that it might prove to be a rollercoaster. "There wasn't paper out of Lausanne. You didn't have a text. You had parameters," the official said, on the condition of anonymity due to the sensitivity of the talks.The official was referring to a framework for a nuclear deal agreed upon in Lausanne, Switzerland, back on April 2. Agreements in principle from Lausanne are now being put to paper, and the official said that, in doing so, the devil has proven to be in the details."You are going to have a text," the official added, noting the "staggeringly consequential" nature of the deal they are about to broker. "It will be evident to everyone what has been agreed."A rally was held on Tuesday in Tehran, attended by supporters of the supreme leader's conditions for a nuclear deal. Those include a rejection of all access to its military sites sought by international inspectors, and immediate sanctions relief upon the signing of a deal.But US negotiators say there will be no "signing." Instead, a deal will involve a phase of adoption, a phase of implementation, and then a phase when all provisions of the deal go live.Russian Foreign Minister Sergey Lavrov, as well as Germany Foreign Minister Frank-Walter Steinmeier, also arrived in Vienna on Tuesday. They both plan on meeting with Kerry and Zarif.