Donald Trump has warned Iran that the US is “ready to help” protesters in the Islamic Republic on a day the country’s clerical regime tightened its clampdown on demonstrations, with claims that 100 “armed rioters” were arrested.

The protests, which started out with economic grievances, have now morphed into one of the biggest challenges the Islamic Republic has faced in its 47-year history.

Protests in Iran are intensifying due to the country's struggling economy, putting pressure on its theocracy as it has shut down the internet and telephone networks.

Several Iranians who protested in Iran over the past few days have spoken to CNN about seeing enormous crowds as well as brutal violence on the streets of Tehran, with one woman saying she saw “bodies piled up on each other” in a hospital.

Iran's Revolutionary Guards warned on Saturday that safeguarding security was a "red line" and the military vowed to protect public property, as the clerical establishment stepped up efforts to quell the most widespread protests in years.

Protests in Iran have continued despite threats from the government to crack down. Online videos show demonstrators protesting Friday night, even after authorities shut down the internet and cut phone lines.

Iranian hospitals reportedly overwhelmed as anti-government protests rage, with doctors treating gunshot wounds to heads and eyes amid nationwide unrest.

The Iranian army said on Saturday it would safeguard strategic infrastructure and public property and urged Iranians to thwart "the enemy's plots", as the clerical establishment steps up efforts to quell the country's biggest protests in years.

In exile for nearly 50 years, Iran's Crown Prince Reza Pahlavi has issued calls urging Iranians to join protests sweeping the country. But support for him may not be clear cut.