Biden tells rally 'we're going to free Iran'

President Joe Biden was "expressing solidarity" with protesters when he said at a campaign event late Thursday that "we're going to free Iran," a White House spokesman clarified on Friday.

The comment sparked an indignant response from the government in Tehran and went beyond the president's previous statements, which had been carefully worded so as not to suggest direct US involvement in the protest movement.

Biden told the California crowd: "Don't worry, we're going to free Iran, they're going to free themselves pretty soon".

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A day later, the White House said Biden was voicing support for the protest movement and not signaling a new approach.

"He was expressing, again, our solidarity with them," said John Kirby, the communications coordinator at the National Security Council.

He said Iran's leadership is "facing problems of their own making".

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"The president's been pretty clear about this... We're going to continue to look for ways to hold the regime accountable for the way that they're treating their own people," he said.

Still, Kirby said the US did not have indications the Iranian regime was on the verge of changing, despite Biden's remark that Iranians were going to "free themselves pretty soon".

Biden made the remark at a campaign event in Southern California for a vulnerable House Democrat after members of the audience raised the subject with a sign on their phone reading, "FREE IRAN".

Protests have spread through Iran after the death of a young woman who was being detained by the country's morality police.

The president has voiced support for the protests and his administration imposed sanctions last month on some Iranian officials for their treatment of protesters.

While the Biden administration has been vocal in its support of Iran's protests, its previous messaging has sought to avoid any implications that the US is involved in directing the current movement in any way.

Iranian authorities have repeatedly tried to blame the US and other foreign governments for the ongoing demonstrations that have gripped the nation since mid-September.

Iran's President Ebrahim Raisi hit back at Biden for voicing his support for the protest movement and promising to "free Iran" during a televised address on Friday.

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"A few hours ago, I was informed that the president of America absentmindedly (said), 'We will soon free Iran.' We were freed 43 years ago, and Iran will never be your milking cow," Raisi said.

"America is aiming to destroy our national unity and coherence. Americans fancy to repeat the experience of Libya, Syria and some other countries, in our country," he continued.