Iran said on Tuesday it had arrested people accused of a role in shooting down a Ukrainian airliner and had also detained 30 people involved in protests that have swept the nation for four days since the military belatedly admitted its error.

Wednesday’s shooting down of Ukraine International Airlines flight 752, killing all 176 people aboard, has led to one of the biggest public challenges to the Islamic Republic’s clerical rulers since they took power four decades ago.

Iran shot down the airliner on Wednesday when its military was on high alert, hours after it had fired missiles at US targets in Iraq. After days of denying a role in the air crash, it admitted it on Saturday, calling it a tragic mistake.

Protesters, many of them students, have held daily demonstrations since then, chanting “Clerics get lost!” and calling for the removal of Supreme Leader Ayatollah Ali Khamenei, in power for more than 30 years.

Police have responded to some protests with a violent crackdown, video posts on social media showed. Footage showed police beating protesters with batons, wounded people being carried, pools of blood on the streets and the sound of gunfire.

Iran’s police denied firing at protesters. The judiciary said 30 people had been detained in the unrest but said the authorities would show tolerance towards “legal protests”.

Iran’s leaders have been facing a powerful combination of pressure both at home and abroad.

Just two months ago, Iran’s authorities put down anti-government protests, killing hundreds of demonstrators in what is believed to be the most violent crackdown on unrest since the 1979 revolution.

Elsewhere in West Asia, where Iran has wielded influence through a network of allied movements and proxies, governments that include powerful Iran-sponsored factions have faced months of hostile demonstrations in Lebanon and Iraq.