PARIS, France (AFP) — The lives of prisoners are at grave risk in Evin prison in Tehran, rights groups warned Sunday, after a fire erupted at the notorious jail as the protest movement sparked by Mahsa Amini's death entered a fifth week.

Gunshots and the sound of explosions were heard during Saturday night's blaze from inside the vast complex in northern Tehran which was smothered by smoke and illuminated by flames, according to footage posted on social media channels.

The fire, the cause of which remains unclear, came as Iran marked one month of protests over the death of 22-year-old Amini, who had been arrested for violating the country's strict dress code for women.

The demonstrations have developed into a movement against the Islamic republic, confronting its clerical leadership with one of its biggest challenges since the ousting of the shah in 1979.

Evin is infamous for the ill-treatment of political prisoners and also holds foreign detainees as well as thousands of people facing criminal charges. Hundreds of those arrested during the demonstrations over Amini's death have reportedly been sent there.