The US president has pledged support for protesters, but Washington is weighing not only how to intervene, but why: to topple the regime in Tehran, to destroy its repressive apparatus or to force it to surrender on the nuclear issue.

Iran has said it will retaliate if the U.S. intervenes amid political unrest in the Middle East country.

U.S. President Donald Trump has been presented with options to intervene in Iran as massive protests there have turned deadly, with hundreds dead and thousands arrested.