Pressure is mounting on Iran to reveal details of its secret nuclear sites and the work that was carried out there. UN nuclear watchdog chief Rafael Grossi will travel to Tehran on Monday to demand access to sites where Iran has stored or used undeclared nuclear material. The focus will be on access to sites from the early 2000s, before Iran signed the Joint Comprehensive Plan of Action, the 2015 deal with world powers to curb the regime’s nuclear program in return for an easing of international sanctions. Iran claims International Atomic Energy Agency (IAEA) inspectors have no right to inspect the sites. “My objective is that my meetings in Tehran will lead to concrete progress in addressing the outstanding questions that the agency has related to safeguards in Iran and, in particular, to resolve the issue of access,” agency director general Grossi said. “I also hope to establish a fruitful and cooperative channel of direct dialogue with the Iranian government which will be valuable now and in the future.” It will be Grossi’s first visit to Iran since he took office last December, and comes amid intense international pressure on the regime over its nuclear program, and tensions between the US and its European allies over Washington’s determination to maintain an arms embargo on Iran and reimpose UN sanctions dating from 2006. Since President Donald Trump pulled the US out of the nuclear deal with Iran in 2018, the other countries involved — France, Britain, Germany, Russia and China — have been struggling to keep it alive. With the reinstatement of US sanctions, Iran’s economy has been steadily deteriorating and Tehran has begun violating provisions of the agreement to try to pressure the other countries to do more to offset those sanctions. The US ratcheted up the pressure last week, and officially informed the UN it was demanding the restoration of all sanctions on Iran. It said Iran was in noncompliance, and invoked a provision of the nuclear deal to “snap back” more sanctions. Russia, China, Britain, France and Germany say the US action is illegal, and it is impossible to withdraw from a deal and then use the resolution that endorsed it to re-impose sanctions. But the US has stuck to its guns, declaring that a 30-day countdown had begun for the snapback of penalties eased after the 2015 deal was signed. The five nations and Iran will meet in Vienna on Sept. 1 to discuss the status of the deal.