Israeli Prime Minister Benjamin Netanyahu and U.S. Secretary of State Marco Rubio spoke as Israel goes on high alert and Iran faces mounting anti-regime protests.

Protests challenging Iran’s theocracy have reached the two-week mark, with demonstrators flooding the streets in Tehran and Mashhad

Iran has warned the US and Israel not to intervene militarily to support protests that have spread across the Islamic republic as President Donald Trump said Washington was “ready to help”.

Tehran threatened on Sunday to retaliate against Israel and U.S. military bases in the event of U.S. strikes on Iran, issuing the warning as Israeli sources said Israel was on high alert for the possibility of any U.

Hundreds of people are believed to have been killed or injured by the security forces, with more than 70 bodies brought to one hospital.

As activists say Iran's anti-government unrest has seen almost 120 people killed, the nation's rulers threaten protesters, and U.S. forces across the Mideast.

Five decades ago, Ayatollah Ruhollah Khomeini became the voice of revolutionary fervour, spurring on demonstrators - even those who wanted a secular system to prevail in Iran. Khomeini's recorded speeches smuggled in on cassette tapes from his exile abroad stoked opposition to Pahlavi's father.

From Crown Prince Reza Pahlavi to imprisoned activists, Iran's potential successors remain unclear. Opposition figures debate who could unify after regime change.

The president has repeatedly warned Iranian authorities that lethal crackdowns on demonstrators would spark a U.S. response.