A United Nations expert has criticized the reimposition of U.S. sanctions on Iran following the withdrawal of the United States from the 2015 nuclear deal between Tehran and world powers, saying they are driving "millions of people into poverty."

UN Special Rapporteur Idriss Jazairy made the comments in an August 22 statement, after the United States earlier this month started reimposing sanctions on the Iranian economy that had been lifted under the nuclear agreement in exchange for curbs on Tehran's nuclear program.

The U.S. move came after President Donald Trump withdrew from the accord in May.

A second round of penalties targeting Iran's crude exports is due to come into effect in early November.

"International sanctions must have a lawful purpose, must be proportional, and must not harm the human rights of ordinary citizens, and none of these criteria is met in this case," said Jazairy, who is serving as UN special rapporteur on the negative impact of the unilateral coercive measures on the enjoyment of human rights.

Calling the U.S. sanctions "unjust and harmful," Jazairy said they are "destroying the economy and currency of Iran, driving millions of people into poverty and making imported goods unaffordable," including "urgently needed humanitarian goods."

The UN expert urged the United States to "demonstrate its commitment to allow agricultural commodities, food, medicine, and medical devices into Iran by taking real and concrete steps to ensure that banks, financial institutions, and companies can quickly and freely be assured that relevant imports and payments are permitted.”

Trump has consistently looked to increase pressure on Tehran to bring about what his administration has called a "change in behavior" regarding its weapons programs and its "destabilizing" activities in the region, accusations Iran denies.

White House national-security adviser John Bolton said on August 22 that the United States was not seeking to topple Iran's government, but said Washington does want authorities in Tehran to change their behavior.

"Just to be clear, regime change in Iran is not American policy. But what we want is massive change in the regime's behavior," Bolton told a news conference in Jerusalem.