Fifty-two people were arrested in Iran’s second city Mashhad on Thursday, the first day of the protests, which also took place in other areas and spread to the capital Tehran as well as Kermanshah the following day.

"There are many reports of peaceful protests by Iranian citizens fed up with the regime’s corruption and its squandering of the nation’s wealth to fund terrorism abroad," the White House added in a statement.

"The Iranian government should respect their people’s rights, including their right to express themselves. The world is watching," it said.

US President Donald Trump has repeatedly taken aim at Iran, denouncing its government as a "fanatical regime" and accusing it of violating an international agreement aimed at curbing Tehran’s nuclear program, refusing to certify its compliance with the deal.

State Department spokeswoman Heather Nauert also addressed the protests.

"The United States strongly condemns the arrest of peaceful protesters. We urge all nations to publicly support the Iranian people and their demands for basic rights and an end to corruption," she said in a statement.