Iran's supreme leader Ayatollah Ali Khamenei on Monday accused arch-foes the United States and Israel of fomenting unrest in the Islamic republic following the death of Kurdish woman Mahsa Amini.

"I say clearly that these riots and the insecurity were engineered by America and the occupying, false Zionist regime, as well as their paid agents, with the help of some traitorous Iranians abroad," he said in his first public comment on the unrest sparked by Amini's death.

"The death of the young woman broke our hearts, but what is not normal is that some people, without proof or an investigation, have made the streets dangerous, burned the Koran, removed hijabs from veiled women and set fire to mosques and cars," the supreme leader added.

Protests have entered their third week since Kurdish Iranian Amini, 22, was pronounced dead on September 16, days after she was detained for allegedly breaching the country's strict dress code.

Speaking at a military graduation ceremony, Khamenei said that the "police are obliged to stand up to criminals and ensure the safety of society".

"Weakening the police means strengthening the criminals. Those who attack the police leave people defenceless against criminals, thugs and thieves."

Iran has repeatedly accused outside forces of stoking the nationwide protests, especially the United States and its allies.

On Friday the intelligence ministry said nine foreign nationals – including from France, Germany, Italy, the Netherlands and Poland – had been arrested. (AFP)