Iran launched advanced uranium enrichment machines on Saturday, a day after US and Iranian officials clashed over what sanctions the US should lift to return to the 2015 nuclear deal.Iran has demanded that all US sanctions since the 2017 be removed.The talks in Vienna, in which European Union officials are shuttling between the remaining parties to the deal and the United States, aim to restore the bargain at the core of the agreement - restrictions on Iran's nuclear activities in exchange for the lifting of US and other international sanctions. "All Trump sanctions were anti-JCPOA & must be removed—w/o distinction between arbitrary designations," Iranian Foreign Minister Javad Zarif said on Twitter, referring to the deal by its full name, the Joint Comprehensive Plan of Action.The US left the JCPOA under former president Donald Trump in 2018; Iran began flouting the deal’s nuclear limitations soon after, having kept its program intact as it had been before the deal, and had ramped up its aggression throughout the Middle East in the years after the JCPOA was reached.The United States says it is prepared to lift "sanctions that are inconsistent with the JCPOA." While it has declined to elaborate, that appears to exclude sanctions formally unrelated to nuclear issues covered by the deal, such as human rights.A senior US State Department official told reporters the United States had seen some signs of Iranian seriousness about returning to the nuclear pact but "certainly not enough." "If Iran sticks to the position that every sanction that has been imposed since 2017 has to be lifted or there will be no deal, then we are heading towards an impasse," the senior US official told reporters on a conference call.Whether the statements are opening gambits or more firm positions remains to be seen. European officials said Iran was bargaining hard at the outset.The remaining parties to the accord - Iran, Britain, China, France, Germany and Russia - met again on Friday after talks formally began on Tuesday and they agreed to keep going, Russian and Chinese envoys said."The #JCPOA participants took stock of the work done by experts over the last three days and noted with satisfaction the initial progress made," Mikhail Ulyanov, Russia's envoy to the United Nations' International Atomic Energy Agency (IAEA), said on Twitter after the meeting formally known as the Joint Commission."The Commission will reconvene next week in order to maintain the positive momentum."The remaining parties have formed two expert-level working groups whose job is to draw up lists of sanctions that the United States will lift and of nuclear restrictions Iran will implement. Their work continues between Joint Commission meetings."All parties have narrowed down their differences and we do see the momentum for gradually evolving consensus," Wang Qun, China's ambassador to the IAEA, told reporters.On Saturday, Iranian state TV aired a live broadcast of Iranian President Hassan Rouhani ordering the new breach of the Joint Comprehensive Plan of Action on Iran’s National Nuclear Technology Day, involving the injection of uranium gas into 164 IR-6 centrifuges, 30 IR-5 centrifuges, and mechanical tests on IR-9 machines with the capacity of 50 early IR-1 machines. “Once again, I stress that all our nuclear activities are peaceful and for non-military purposes,” Rouhani said in televised remarks.“We continue to be committed to our pledge to NPT (non-proliferation treaty) and to the world not to deviate militarily from our nuclear program,” Rouhani said.The UN atomic watchdog flagged another breach by Iran on Friday, a report by the agency seen by Reuters showed, likely raising tensions with Western powers.The International Atomic Energy Agency avoids saying Iran has breached the deal. At the same time, it generally only issues such ad hoc reports to member states in the event of a breach. Two diplomats told Reuters what the report described amounted to a fresh breach.The breach has to do with what counts officially towards Iran's stockpile of enriched uranium, a highly sensitive issue since that stockpile could be enriched further to weapons-grade material suitable for nuclear bombs if Iran chose to do so.After the deal was reached in 2015 the parties to it defined what should count towards the stockpile, and excluded items such as scrap fuel plates with uranium enriched to near 20% fissile purity, which were deemed "unrecoverable." Friday's report, however, said Iran had recovered some of that material.While the amount of enriched uranium extracted is small, it amounts to a fresh breach at a delicate stage.After talks among the remaining parties to the deal wrapped up on Friday, France's Foreign Ministry said a "positive" first week of negotiation should not be undermined by new Iranian provocations."In this context, it is all the more important that Iran refrain from any further violation of its nuclear commitments that could undermine the current dynamic," Foreign Ministry spokeswoman Agnes von der Muhll told reporters.David Albright, a former UN weapons inspector and a hawk on Iran, said the latest breach also raises questions about what major powers excluded from the enriched uranium stockpile."Looking back, exempting this near 20% enriched uranium scrap was probably not a good idea," he said, explaining what scrap means in this case: "When enriched uranium is made into fuel plates, some does not get used, somewhat like batter for a cake."Last week, in response to a State Department remark that the US is “prepared to take the steps necessary to return to compliance...including by lifting sanctions that are inconsistent with the JCPOA," a senior official in Jerusalem expressed concern that reduced pressure on Iran will not moderate its position.“One of our problems with the American position,...is that, if you ask people here in the region, the Iranians have moderated their position only when there has been persistent and determined pressure on them," the Israeli official said. “Lifting the leverage that you have…is not the way to get the Iranians to moderate their position.”Lahav Harkov contributed to this report.