Irvine, California - President Joe Biden has called on Iran's leaders not to take violent action against protesters in the country, and said he is "stunned" by the mass protests of "brave women."

Iran has been swept by protests for weeks following the death of 22-year-old Mahsa Amini in mid-September, who was detained by the morality police in Tehran for violating the country's strict dress regulations for women.

Biden was "stunned" by the mass protests and said the US stands with Iran's "brave women", he said during an appearance in the California city of Irvine on Friday.

"Iran has to end the violence against its own citizens simply exercising their fundamental rights," Biden said.

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"It stunned me what it awakened in Iran. And it’s awakened something that I don’t think will be quieted in a long, long time."

Biden said women and men should have the right to freedom of expression and assembly.

"Women all over the world are being persecuted in various ways. But they should be able to wear, in God’s name, what they want to wear. No one should be telling them what to wear," he added.

Since Amini's death there have been nationwide and international protests against Iran's leadership and specifically the headscarf mandate.

Security forces have responded with a deadly crackdown and an internet shutdown, with dozens said to have been killed and many more injured. The country's leaders have blamed the unrest on a US conspiracy.

The US has slapped Iranian leaders with sanctions over the government's violent suppression of protests.