Watch: United States to end waivers on Iranian oil sanctions for five countries

The Trump administration on Monday told five nations, including allies Japan, South Korea and Turkey, that they will no longer be exempt from U.S. sanctions if they continue to import oil from Iran.

President Donald Trump has decided not to reissue the waivers when they expire in early May, White House press secretary Sarah Sanders said.

"The decision is intended to bring Iran's oil exports to zero, denying its principal source of revenue," Sanders said in a statement.

Secretary of State Mike Pompeo claimed the sanctions have already cost Iran around $10 billion, as he told a press conference the US would not grant anymore exemptions.

"Any nation interacting with Iran should do its due diligence and err of the side of caution. The risks are simply not going to be worth the benefits," he said.

Pompeo said the U.S. had gained assurances from oil producers - namely Saudi Arabia and the UAE - to ensure a sufficient supply to minimise impact on pricing.

He added the length of the sanctions being at zero depends on the Iranian Ayatollah and "his cronies" meeting certain demands.

These demands include Iran ending its pursuit of nuclear weapon, stopping development of ballistic missiles, stopping sponsoring and committing terrorism and stopping arbitrary detention of US citizens.

Read more: China opposes US sanctions strategy and says bilateral cooperation with Iran is legal