Less than a year after the landmark nuclear deal came into effect, Iran was on the verge of another unlikely diplomatic breakthrough. And one of the country's most powerful arsenals remains locked away deep in the bowels of a dimly lit state-owned building in Tehran, hidden from the world's eyes. Some might call that a tragedy. Because by any measure, the collection held at the Tehran Museum of Contemporary Art is exceptional, the greatest outside the West.

Some of the world's most expensive and rarely seen modern art, including works by the Americans Jackson Pollock and Andy Warhol, went on display Saturday in a major exhibition in Iran.