In a statement Sunday, the State Department said the decision not to renew the waiver was made to "ensure we do not allow Iran any degree of economic or financial relief."

The move comes two days after Trump said he had written Iran's supreme leader Ayatollah Ali Khamenei to press for new talks on Tehran's nuclear program.

The US president warned of possible military action if Iran did not give in -- a message that prompted Khamenei to reject "bullying" by foreign powers.

Iran supplies a third of Iraq's gas and electricity, providing Tehran with substantial income.

- 'Never take place' -

The Iranian mission to the United Nations on Sunday suggested Tehran might be willing to discuss certain issues -- but not the complete end of its nuclear program.

"If the objective of negotiations is to address concerns vis-a-vis any potential militarization of Iran's nuclear program, such discussions may be subject to consideration," said a statement from the mission.

"However, should the aim be the dismantlement of Iran's peaceful nuclear program to claim that what Obama failed to achieve has now been accomplished, such negotiations will never take place."

The waiver was introduced in 2018, when Washington reimposed sanctions on Tehran after Trump abandoned a nuclear deal with Iran negotiated under President Barack Obama.

Since returning to the White House in January, Trump has reinstated his policy of exerting "maximum pressure" against Iran.

"The President's maximum pressure campaign is designed to end Iran's nuclear threat, curtail its ballistic missile program, and stop it from supporting terrorist groups," a spokesman for the US embassy in Baghdad said earlier Sunday.

The spokesman urged Baghdad "to eliminate its dependence on Iranian sources of energy as soon as possible."

The landmark 2015 deal that Obama helped negotiate between Tehran and major powers promised sanctions relief in return for Iran curbing its nuclear program.

Tehran, which denies seeking nuclear weapons, initially adhered to the nuclear deal after Trump pulled out of it, but then rolled back commitments.

US officials estimate Iran would now need mere weeks to build a nuclear bomb if it chose to.

- 'All scenarios' -

Trump pulled out of the agreement over the objections of European allies, instead imposing sweeping US sanctions on any other country buying Iran's oil. The waiver was extended to Iraq as a "key partner" of the US.

Iraq, despite having immense oil and gas reserves, remains dependent on such energy imports. But Baghdad said it had prepared "for all scenarios" regarding the waiver.

The ending of the energy waiver is expected to worsen the power shortages that affect the daily lives of 46 million Iraqis.

Gulf analyst Yesar Al-Maleki of the Middle East Economic Survey (MEES) said Iraq will now face challenges in providing electricity, especially during summer.

To alleviate the impact, Iraq has several options including increasing imports from Turkey.