The United States and Iran on Thursday clashed openly at the U.N. atomic watchdog for the first time since they signed a landmark nuclear deal last year, differing over Tehran’s repeated testing of one of the deal’s less strictly defined limits.

The International Atomic Energy Agency (IAEA), which is policing the deal, said Iran’s overstepping of the limit on its stock of a sensitive material for the second time this year risked undermining countries’ support for the agreement. Continue Reading.