PARIS, France (AFP) — Iran's judiciary authority said Monday that eight prisoners were killed in a fire that raged amid unrest inside Tehran's Evin prison, doubling the previously reported death toll.

The blaze Saturday night, which Iran said broke out amid "riots and clashes" came after four weeks of protests over the death of 22-year-old Masha Amini, following her arrest for allegedly violating Iran's strict dress code for women.

The wave of demonstrations has turned into a major anti-government movement in the Islamic republic, confronting its clerical leadership with one of its biggest challenges since the ousting of the shah in 1979.

After four Evin prison inmates injured in the fire died in hospital, "the total number of victims of the fire and the clash between prisoners has reached eight," the judiciary's Mizan Online website said.

Gunshots and explosions were heard during the blaze from inside the complex, illuminated by flames and smothered by smoke, in video footage posted on social media channels.

Prisoners' relatives and rights groups have voiced grave fears for other inmates and said authorities had used tear gas at the facility.

Evin, infamous for the ill-treatment of political prisoners, also holds foreign detainees and thousands facing criminal charges.

Hundreds of those arrested during the recent demonstrations and in a crackdown on civil society have been sent there.