It started with something as innocent as waving a rainbow flag. Now dozens of LGBT people have been arrested in in Egypt in one of the country's biggest crackdowns on LGBT rights.

On September 22, concertgoers waved Pride flags at a Mashrou’ Leila concert at Cairo Festival City in New Cairo. (Lead singer Hamed Sinno is openly gay and some of the band’s songs address queer themes.)

After images of the flags surfaced on social media, police used security-camera footage to identify and arrest participants. Days later, the Supreme Council for Media Regulation (SCMR) prohibited any positive depiction of the LGBT community in the media and Mashrou’ Leila was banned from performing in the country again.

Now, Amnesty International reports, police have started a manhunt against homosexuals and those who support gay rights: Some 57 people—including at least one woman—have been arrested in Cairo, Giza, and Damietta on charges ranging from “debauchery" and "inciting sexual deviancy" to "joining an outlawed group." Nine have received prison sentences, and an additional 35 are facing trial. (Several detainees have been subjected to forced anal examinations.)

“The scale of the latest arrests highlights how dangerously entrenched homophobia is within the country,” said Amnesty International’s Najia Bounaim.  “The Egyptian authorities’ announcement that they are investigating the rainbow flag incident as a criminal act is utterly absurd. No one should be punished for expressing solidarity with LGBT individuals or based on their perceived sexual orientation.”

Homosexuality is not technically illegal in Egypt, but laws like the ones against debauchery are often used to persecute LGBT Egyptians. (Parliament is considering criminalizing same-sex relations with up to 15 years in prison.) The current clampdown is the most severe since 2001, when 52 men were arrested at a floating gay nightclub. (Gay Star News reports many LGBT activists have fled Cairo, with a number of people leaving the country altogether.)

“The Egyptian government, by rounding people up based on their presumed sexual orientation, is showing flagrant disregard for their rights.” said Human Rights Watch’s Sarah Leah Whitson. “Egypt should stop dedicating state resources to hunting people down for what they allegedly do in their bedrooms, or for expressing themselves at a rock concert, and should instead focus energy on improving its dire human rights record.”

Mashrou’ Leila is urging for international pressure on the Egyptian government “to immediately halt its ongoing witch-hunt and release all detainees.”

‘We cannot begin to explain how saddened we are to see yet another era of backwards tyranny creep over one of our most beloved countries and audiences," the band said in a statement. "This crackdown is by no means separable from the suffocating atmosphere of fear and abuse experienced by all Egyptians on a daily basis, regardless of their sexual orientations."