US Secretary of State Mike Pompeo speaks at a news conference to announce the Trump administration's plan to designate Iran's Revolutionary Guard a "foreign terrorist organization," at the US State Department in Washington. File picture: Patrick Semansky/AP

Washington - The United States said on Monday it will not extend waivers to eight countries that have been allowed to buy oil from Iran despite US sanctions that went into effect in November.

The White House said the move is "intended to bring Iran's oil exports to zero, denying the regime its principal source of revenue."

The eight countries affected are China, India, Italy, Greece, Japan, South Korea, Taiwan and Turkey. They were granted a six-month waiver in November allowing them to continue importing Iranian oil. Monday's announcement means that period will not be extended beyond its May 2 expiration.

The sanctions are part of a pressure campaign against Iran, the country that US President Donald Trump sees as behind the most intractable problems in the Middle East. They were imposed in November after Trump decided unilaterally to withdraw the US from the 2015 Iran nuclear deal negotiated and signed with Iran by the US, Britain, France, China, Russia and Germany.

The agreement, which Iran and the other countries continue to abide, places strict limits on Iran's nuclear programme to prevent the country from building nuclear weapons. Iran agreed to the deal in exchange for the lifting of previously imposed sanctions.

US Secretary of State Mike Pompeo said the US sanctions that took effect in November have deprived Iran of billions of dollars it would have used to fund terrorist organizations, develop missiles and back rebels in Yemen.

Pompeo told reporters at the State Department that any country that tries to get around the sanctions will find that "the risks are simply not going to be worth the benefits."

Israeli Prime Minister Benjamin Netanyahu welcomed the decision, saying it is "of great importance for increasing pressure on the Iranian terror regime."

In a statement released by his office, Netanyahu added: "We stand by the United States' determination against the Iranian aggression and this is the right way to stop it."

When the six-month waivers were granted in November, Pompeo justified them by saying that the US was looking "to ensure a well-supplied oil market." On Monday, he said steps were taken to ensure market stability before the decision not to extend the waivers.