Ever since European seaports closed their gates to Iranian oil tankers last summer, Iran has looked to the East to keep its economy afloat. Countries such as China, India and South Korea — some of them critics of Western sanctions — have offered Iran a lifeline of reliable markets and much-needed dollars.

But perhaps not for long. In two weeks, the White House will begin enforcing a little-noticed statute that could dry up one of Iran's largest remaining sources of oil income, U.S. officials say.

Beginning Feb. 6, Iran still will get paid for the oil it delivers to Asian markets, from Mumbai to Shanghai to Busan — only not in cash.