The UN’s nuclear watchdog is readying itself for a showdown with Tehran over Iran’s continued stonewalling on access to two sites possibly linked to an old, clandestine nuclear weapons programme. Since he became the head of the International Atomic Energy Agency (IAEA) last year, Rafael Grossi has been grappling with Iran’s decision to renege on commitments under its 2015 nuclear deal with world powers. Now central to the disagreement, which lies at the heart of tensions between the United States and Iran, is access to two sites that the agency believes is linked to a secret nuclear programme that was discontinued in 2003. Mr Grossi, who has been seen to take a more confrontational approach with Iran over the past months, has now warned of repercussions if Tehran does not grant access to the sites by the end of the month. "It will be bad," he told <em>The Wall Street Journal.</em> "I keep insisting on the absolute necessity for us to resolve this issue very soon." Iran has refused to acquiesce to requests for access to the locations after the IAEA head accelerated a probe in January over undeclared nuclear material. Information gleaned from an archive of Israeli-obtained intelligence on Iran’s past nuclear activity has given the UN watchdog further insight into the Islamic Republic’s previous activities before 2015. The IAEA’s insistence over the old sites and Iran’s intransigence now threatens to deliver a serious blow to the already faltering 2015 accord, known as the Joint Comprehensive Plan of Action. The US, which withdrew from the deal in 2018, has called on Mr Grossi to update IAEA members soon over Iran’s co-operation. Tehran’s continued non-compliance would allow the US to attempt to take Iran to the UN Security Council over the issue, though it would likely face strong opposition from Russia and China. However, with Mr Grossi at the helm of the IAEA the agency has sought to investigate Iran’s activities prior to 2015, but the Islamic republic has since July 2019 steadily broken the terms of the nuclear deal. The US withdrawal from the agreement, whereby Tehran agreed to give up its nuclear weapons ambitions in exchange for relief on economic sanctions, has been the impetus for a series of incidents between the US, Iran and their respective allies. The US quit the deal in 2018 saying Iran was failing to live up to the spirit of the agreement by carrying out ballistic missile tests and backing proxies in a number of regional conflicts. The remaining signatories – China, France, Russia, the UK, and Germany – have attempted to salvage the deal but in the intervening months relations between the US and Iran have continued to deteriorate. US President Donald Trump has sought to impose a campaign of "maximum pressure" against Iran after his predecessor, Barack Obama, pursued a policy of relative rapprochement. The US, which backed Mr Grossi’s candidacy for the IAEA’s top post, has continued to show its support for the direction of his leadership. “I think that Director General Grossi has brought new energy to the agency – new transparency,” US IAEA ambassador Jackie Wolcott said. However, other nations fear that an end to the nuclear accord could result in a more combative Iran and inevitably lead to a resumption of the country’s nuclear programme. China has hit out at the IAEA head’s June report and Russia has complained that the activities the watchdog seeks to investigate lie too far in the past. Nevertheless, Mr Grossi has said his investigators must be given access. His one-month time frame for compliance falls before an October deadline on the end an existing Iran weapons embargo, another flashpoint in the diplomatic standoff with Tehran. The end of the arms embargo, a guarantee of the nuclear deal, is one of the few face-saving benefits of the agreement to which Iran has been able to cling since the US withdrawal. The US has vowed to slap further sanctions on Iran if Security Council members do not vote to extend the embargo, a measure that also presents an existential threat to the accord.