Iran has alleged that they have blocked the United Nations nuclear inspector from a nuclear site after they tested positive for suspected traces of explosive nitrates. The Iranian Atomic Energy Organisation said in a statement posted online said that the inspector triggered an alarm last week at the entrance to the Natanz uranium enrichment plant due to carrying a "suspect product". On Wednesday, Iran injected uranium gas into centrifuges at its underground Fordow nuclear complex, taking its most-significant step away from its 2015 nuclear deal with world powers. These latest steps put additional pressure on Europe to offer Iran a way to sell its crude oil abroad despite the U. sanctions imposed on the country since President Donald Trump unilaterally withdrew America from the nuclear deal over a year ago. The gas injection began after midnight at Fordow, a facility built under a mountain north of the Shiite holy city of Qom, the Atomic Energy Organization of Iran said. A UN official from the IAEA witnessed the injection, it said. The centrifuges ultimately will begin enriching uranium up to 4.5 per cent, which is just beyond the limits of the nuclear deal, but nowhere near weapons-grade levels of 90 per cent. Fordow’s 1,044 centrifuges previously spun without uranium gas for enrichment under the deal, which saw Iran limit its uranium enrichment in exchange for the lifting of economic sanctions. The deal had called for Fordow to become “a nuclear, physics and technology centre.” Iran acknowledged Fordow’s existence in 2009 amid a major pressure campaign by Western powers over Tehran’s nuclear programme. The West feared Iran could use its programme to build a nuclear weapon; Iran insists the programme is for peaceful purposes. Meanwhile, the Atomic Energy Organization of Iran said it had blocked a female IAEA inspector from its facility at Natanz, where centrifuges also enrich uranium. Iran said an alarm went off while the woman tried to enter the facility, causing officials there to stop here from going in. The state-run IRNA news agency, citing Iran’s atomic agency, said the woman was stopped “due to concerns over carrying suspicious materials.” The inspector later left Iran without completing her visit, it said. This marks the first known time of Iran blocking an inspector amid the tensions. Iran said it planned to address its decision to block the inspector at a meeting of the IAEA Thursday in Vienna. Iranian officials repeatedly have stressed the steps taken so far, including going beyond the deal’s enrichment and stockpile limitations, could be reversed if Europe offers a way for it to avoid U.S. sanctions choking off its crude oil sales abroad. However, a European trade mechanism has yet to take hold and a French-proposed US$15 billion line of credit has not emerged. The collapse of the nuclear deal coincided with a tense summer of mysterious attacks on oil tankers and Saudi oil facilities that the U.S. blamed on Iran. Tehran denied the allegation, though it did seize oil tankers and shoot down a U.S. military surveillance drone.