What will China and India do without Iran's oil?
Despite its thirst for oil, Japan reduced imports from Iran after a request from the US.
As a result it was exempt from US sanctions which aim to punish countries that continue to trade with Iran.
But other nations including China, India and South Korea were left exposed. They have until the end of June to show that they're cooperating - or face being cut off from the US financial system. So what would that mean for them?
We hear first from our correspondent in Shanghai, John Sudworth and then from Mumbai, Rajini Vaidyanathan.