Tehran, Iran - The US government will impose further sanctions on senior security officials in Iran after a woman died in custody, sparking an ongoing uprising. Iranian supreme leader Ayatollah Ali Khamenei has blamed the unrest in the country on a "conspiracy" involving the United States, Israel, and "Iranian traitors abroad."

President Joe Biden was "gravely concerned about reports of the intensifying violent crackdown on peaceful protestors in Iran, including students and women, who are demanding their equal rights and basic human dignity," he said in a statement.

Later this week, the US will announce further sanctions "on perpetrators of violence against peaceful protestors," Biden said.

"We will continue holding Iranian officials accountable and supporting the rights of Iranians to protest freely."

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Hundreds of thousands of people across Iran have been demonstrating against the government since the death of Mahsa Amini, a 22-year-old woman.

She was arrested on September 13 by the morality police for violating the strict Islamic dress code. Iran's strict interpretation of the Koran requires women to cover their hair and almost all skin, except their faces.

Amini died in hospital on September 16 after having fallen into a coma but the cause of her death remains unknown.

Witnesses in the capital Tehran have said both security forces and protesters have become increasingly violent. Yet, Iran's supreme leader Ayatollah Ali Khamenei has pinned the blame on the US and Israel.

"A young woman died and that was very bitter and regrettable," Khamenei said on Monday in his first reaction to the case of Amini and the ongoing protests across the country.

But it was neither normal nor acceptable to torch Korans, mosques, cars, and banks for this reason and to tear headscarves from women's heads, the supreme leader asserted.

"These riots are an operation programmed by the US, the Zionist regime (Israel), and Iranian traitors abroad to torpedo the security of the country," the cleric said.

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The US and the West are concerned neither with Amini nor with the headscarf requirement in Iran, he added.

"No one in the United States mourns the dead woman, it's all about the independence of the Islamic Republic and its resistance (against the United States)," Khamenei told state broadcaster IRIB.

He added that the Americans and Iran's enemies wanted to break this resistance and make the country once again dependent on the West.

As violent unrest continues to rock the country, classes have been suspended until further notice at Iran's Sharif University. Starting Monday, classes will only take place online, the Aftab News portal reported.

According to university students, that plan is hardly feasible because of internet blocks that have been imposed in connection with the protests.

Witnesses in the capital Tehran have said both security forces and protesters have become increasingly violent in the last weeks. According to local media reports, security forces targeted Sharif students late on Sunday. Police officers and militias sealed off the campus overnight.

Several professors at the elite university have been beaten, the Iranian news portal Emtedad reported.

On social media, users spoke of a police attack and "civil war-like" conditions.

The Iranian media dismissed these reports as exaggerated anti-government sentiment.