Iran summoned Britain’s ambassador for the second time since nationwide protests erupted last month, Iranian media said on Wednesday, stepping up accusations of a Western role in unrest sparked by young woman Mahsa Amini’s death in police custody.

Iran has accused adversaries including the United States of orchestrating the unrest, which marks the biggest challenge to the country’s clerical elite in years with protesters calling for the downfall of the Islamic Republic.

People across Iran have joined protests since Amini, 22, died in the custody of morality police who detained her in Tehran on September 13 for “inappropriate attire”.

Videos shared on social media on Wednesday showed high school girls in Tehran taking off their headscarves and chanting “death to (Supreme Leader Ayatollah Ali) Khamenei”.

The authorities are waging a deadly crackdown to suppress the unrest, even if observers do not believe the Shi’ite clerical establishment is close to being toppled, 43 years after the country’s Islamic Revolution.

Witnesses said that riot police were deployed heavily in several cities on Wednesday, particularly around universities – a focal point of protests.

“There are lots of security forces around Tehran University. I am even scared to leave the campus. Lots of police vans are waiting outside to arrest students,” a Tehran student said.

The British envoy, previously summoned, was summoned again on Tuesday in reaction to “interventionist comments” from the British foreign ministry, Iranian state media reported.

A senior foreign ministry official said “unilateral statements” by Britain showed it had “a role in the belligerent scenarios of terrorists active against the Islamic Republic”, Tasnim news agency said, without elaborating on the accusations.

Amini’s death and the crackdown on protests have compounded tensions in Tehran’s already difficult relations with Western powers, deepening rifts at a time when negotiations to revive Tehran’s 2015 nuclear deal have stalled.

Britain’s foreign ministry said on Monday it had summoned Iran’s charge d’affaires over the crackdown, during which rights groups say thousands have been arrested and hundreds injured, putting the death toll at over 150.

The United States has said it will impose “further costs” on Iranian officials responsible for violence against protesters.

The Basij, a volunteer militia affiliated with Iran’s Revolutionary Guards, has played a big role alongside police. Authorities have reported numerous deaths among the security forces.

Iran has accused the United States of seeking to use the unrest to destabilise the country, blaming armed dissident groups – among others – for violence. But many Iranians, including celebrities, have taken part or offered support for the protests.

In footage said to have been filmed at a school in Shiraz on Tuesday, about 50 female pupils surrounded a member of the Basij who had been invited to give a speech, shouting “Basij get lost” and “death to Khamenei”.

Underlining unbending views in the government, Interior Minister Ahmad Vahidi accused demonstrators of creating “hideous scenes” in the name of women’s rights. Defending the Islamic Republic’s conservative dress code, he said protesters saw “freedom in the nakedness and shamelessness of women”.

In France, leading actresses including Juliette Binoche and Isabelle Huppert cut locks of their hair in protest at Amini’s death, and a Swedish member of the European parliament snipped off her ponytail while giving a speech.

Iran’s chief prosecutor criticised the Amini family lawyer for making statements “without evidence”, after he was quoted as saying that “respectable doctors” believe she was physically beaten in custody.

President Ebrahim Raisi has ordered an investigation into her death.