Iran's stock of uranium enriched to 60% is now almost three times the roughly 42kg that by the IAEA's definition is theoretically enough, if enriched further, to produce a nuclear bomb.

Japan's nuclear regulator granted approval for plant operator Tokyo Electric Power to start releasing the water - which Japan and the IAEA say is safe but nearby countries fear it may contaminate food.

Seoul announced its own assessment after the IAEA gave the greenlight to Japan's plan, despite concerns over safety in some neighbouring countries and signs of a consumer backlash.

While indirect talks between Iran and the US on reviving the 2015 Iran nuclear deal have stalled, Tehran has increased the number of advanced centrifuges the deal bans it from using to produce enriched uranium.