U.S. and European sanctions targeting the Iranian energy sector went into force during the summer. The U.S. government issued a series of waivers for countries that displayed a "significant" cut back on crude oil purchases from Iran, however.
Clinton said, in a statement, that Japan has taken such steps and would be shielded for 180 days from Sept. 14.
"Japan has ... taken significant steps to reduce its crude oil purchases, which is especially notable considering the extraordinary energy challenges it has faced in the aftermath of the Fukushima disaster," she said.
A magnitude-9 earthquake and tsunami in Japan last year triggered a meltdown at the Fukushima Daiichi nuclear power station. The country as a result was forced to take on more oil and natural gas to balance its energy needs.
The Platts news service in June forecast that Japan's crude and fuel oil demand for power generation was expected to be around 700,000 barrels per day from July through September.