Growing public fury over woman's death in police custody
Khamenei says Amini's death 'deeply broke my heart'
Supreme leader blames foreign foes for 'riots'
Anti-government protests spread to universities
(Adds more protests, UK summons Iran envoy, U.S. reaction)
By Parisa Hafezi
DUBAI, Oct 3 (Reuters) - Iran's supreme leader on Monday gave his full backing to security forces confronting protests ignited by the death of Mahsa Amini in custody, comments that could herald a harsher crackdown to quell unrest more than two weeks since she died.
In his first remarks addressing the 22-year-old's death after her arrest by morality police over "inappropriate attire", Ayatollah Ali Khamenei said Amini's death "deeply broke my heart" and called it a "bitter incident" provoked by Iran's enemies.
"The duty of our security forces, including police, is to ensure the safety of the Iranian nation ... The ones who attack the police are leaving Iranian citizens defenceless against thugs, robbers and extortionists," Khamenei told a group of armed forces cadets in Tehran.
Security forces, including police and the volunteer Basij militia, have been leading a crackdown on the protests, with thousands arrested and hundreds injured, according to rights groups, which put the death toll at over 130.
Iranian authorities have reported many members of the security forces killed during the unrest, which has spiralled into the biggest show of opposition to Iran's authorities in years, with many calling for the end of more than four decades of Islamic clerical rule.
Khamenei said security forces had faced "injustice" during the protests.
"Some people have caused insecurity in the streets," Khamenei said, sharply condemning what he described as planned "riots", and accusing the United States and Israel - the Islamic Republic's arch-adversaries - of orchestrating the disturbances.
The harsh crackdown against the protests has drawn widespread international condemnation. The White House denounced the crackdown and Britain summoned the Iranian charge d’affaires, condemning the crackdown as "truly shocking".
Within hours after Amini's funeral in the Kurdish town of Saqez on Sept. 17, thousands of Iranians poured into the streets across the country, with people burning pictures of Khamenei and chanting "Death to the dictator", according to videos on social media.
Still, there is little chance of a collapse of the Islamic Republic in the near term, since its leaders are determined not to show the kind of weakness they believe sealed the fate of the U.S.-backed Shah in 1979, officials and analysts told Reuters.
However, the unrest calls into the question the priority that has defined Khamenei's rule - the survival at any cost of the four-decade-old Islamic Republic and its religious elite.
"Those who ignited unrest to sabotage the Islamic Republic deserve harsh prosecution and punishment," said Khamenei.
The protests have not abated despite a growing death toll and an increasingly violent crackdown by security forces using tear gas, clubs and - in some cases, according to videos on social media and rights groups - live ammunition.
In defiance of Khamenei's warning, Iranians in several cities chanted "We want regime change" and "death to Khamenei" from rooftops at night - a form of protest used in the 1979 revolution that turned Iran into an Islamic Republic.
In an unprecedented move, high school students in a dozen cities joined the protests, refusing to attend classes and walking in the streets without compulsory headscarf. Videos on social media showed young girls chanting "Freedom, Freedom" in the city of Karaj.
Demonstrations also spread to dozens of universities, with university students staging strikes to protest a late Sunday attack by security forces at Tehran's prominent Sharif University. Dozens of students were arrested and many have been injured according to social media posts and videos. (Reporting by Parisa Hafezi; Writing by Tom Perry and Parisa Hafezi; Editing by Toby Chopra, Mark Heinrich and Grant McCool)