Dubai, June 26 -- As Iran prepares to surpass limits set by its 2015 nuclear deal with world powers, each step it takes narrows the time the country's leaders would need to have enough highly enriched uranium for an atomic bomb - if they chose to build one.

The United Nations says Iran has so far respected the deal's terms. But by Thursday, Iran says it will have over 300 kilograms (660 pounds) of low-enriched uranium in its possession, which would mean it had broken out of the atomic accord.

European countries that are still a part of the nuclear accord face a July 7 deadline imposed by Tehran to offer a better deal and long-promised relief from U.S. sanctions, or Iran will also begin enriching its uranium closer to weapons-grade level...