President Donald Trump on Friday condemned the arrest of protesters in Iran, telling Tehran that "the world is watching" as officials reported fresh demonstrations over economic hardships, corruption and regional interventions.

Scores were arrested in Tehran and other cities on Friday, after 52 were detained on the first day of protests on Thursday.

"Many reports of peaceful protests by Iranian citizens fed up with regime's corruption & its squandering of the nation's wealth to fund terrorism abroad," Trump tweeted.

"Iranian govt should respect their people's rights, including right to express themselves. The world is watching! #IranProtests."

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.

The U.S. State Department and the White House also issued statements condemning the arrests of protesters in Iran and demanding that Tehran allow free expression by the people.

"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," said White House spokeswoman Sarah Sanders.

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

The State Department's spokeswoman said U.S. Secretary of State Rex Tillerson was personally urging support for what he has described as "elements inside of Iran that would lead to a peaceful transition of government."

"We urge all nations to publicly support the Iranian people and their demands for basic rights and an end to corruption," said spokeswoman Heather Nauert.