China and India are among countries that have dodged US sanctions by cutting back on Iranian crude, Washington said Friday as it pledged to "aggressively" enforce such punitive measures despite a recent nuclear deal with Tehran.

President Barack Obama determined that global crude production was enough "to permit foreign countries to reduce significantly their purchases of Iranian oil" after taking note of a report on the topic, the White House said.

"In this context, it is notable that many purchasers of Iranian crude oil continue to reduce, or have ceased altogether, their purchases from Iran," it added.

This biannual evaluation is mandated by a 2012 law aimed at drying up Tehran's oil revenues by forcing third countries to stop buying Iranian crude or face sanctions.

But the law allows the US executive branch to grant waivers to states that cut back on their purchases.

"I am pleased to announce that, based on additional significant reductions in the volume of their purchases of Iranian crude oil, China, India, the Republic of Korea, Turkey, and Taiwan have again qualified for an exception to sanctions," Secretary of State John Kerry said in a statement.

The top US diplomat also noted that Malaysia, South Africa, Singapore, and Sri Lanka have also avoided sanctions "because they no longer purchase crude oil from Iran."

The announcement comes less than a week after world powers -- the five permanent members of the United Nations Security Council and Germany known as the P5+1 -- reached a historic deal with Iran on its disputed nuclear program.

Pending negotiations for a broader agreement, the Islamic state agreed to freeze parts of its program in exchange for an estimated $7 billion of relief from crippling sanctions.

"The effectiveness of the international sanctions regime has proven essential in bringing Iran to the table to negotiate," Kerry said.

However, he added, the interim November 24 deal struck in Geneva does not provide sanctions relief for countries who up their Iranian crude purchases or for potential new customers.

"We will continue to aggressively enforce our sanctions over the next six months, as we work to determine whether there is a comprehensive solution that gives us confidence that the Iranian nuclear program is for exclusively peaceful purposes," he said.