The seven had again qualified for an exception to the sanctions "based on additional significant reductions in the volume of their crude oil purchases from Iran or for reducing those purchases to zero and remaining there", he wrote.
"Today's determination is another example of the international community's strong and steady commitment to convince Iran to meet its international obligations," Kerry added.
A total of 20 countries and economies have continued to significantly reduce the volume of their crude oil purchases from Iran or have completely eliminated such purchases.
The other economies the State Department renewed waivers for were South Korea, Malaysia, Singapore, South Africa, Sri Lanka, Turkey and Taiwan. Japan and 10 EU countries got waivers earlier this spring.
China remains Iran's top trading partner and its No. 1 client for petroleum exports, with Japan, India and South Korea among the other top purchasers.
President Barack Obama Monday issued an executive order imposing sanctions on foreign financial institutions that facilitate deals in the rial, which has lost two-thirds of its dollar value since late 2011.
New legislation that could further limit Iran's oil sales and reduce Tehran's access to its foreign currency accounts is also reported to be on the anvil.