Insein Prison in Rangoon, which houses many political prisoners as well as ordinary criminals, took a direct hit from Cyclone Nargis, which tore through the ramshackle facility at midnight on Friday, ripping zinc roofs from its buildings. The jail, which was built in British colonial times, consists of long cell blocks radiating from a central hub. Common criminals are held in huge rooms that can contain 100 people, while political prisoners are crammed into cells measuring six feet by eight.

The prison administration reacted to the cyclone with the same lethargy as regime authorities outside the prison, who reportedly took no action to help communities in the path of the cyclone. According to the Assistance Association for Political Prisoners (AAPP), based in Mae Sot on the Thai-Burma border, more than 1,500 prisoners were herded into a hall within the prison and locked in until the morning, while the cyclone raged around them. In the morning they were "wet, cold and hungry as well as angry", AAPP reported. "Even though prisoners requested prison guards to open the doors and move them to safety, the authorities ignored their request. Some prisoners set fire to the prison hall and a riot ensued."

Prison guards called in soldiers and riot police and opened fire on the prisoners, killing 36 outright and injuring 70. Among the political prisoners held in Insein is Min Ko Naing, Burma's most famous political prisoner after Aung San Suu Kyi. He is an organiser of the uprising of 1988, the biggest challenge to military rule in the 46 years since the army came to power. The uprising was crushed and thousands of protesters killed.

Min Ko Naing went into hiding but was arrested and given a long jail term. He was released in 2004 and resumed organising resistance. He was one of the participants in the mute protest against fuel price rises in Rangoon in August which prompted the mass demonstrations by Buddhist monks in September. He was again arrested and given another long jail sentence.

Burmese democracy activists have been warning for months that Min Ko Naing is suffering from an eye infection which could lead to blindness if not treated. He and other political prisoners were threatened by the choking smoke from the burning prison hall, which spread to the tiny cells. Guards let them out "just in time", according to AAPP. "One political prisoner was immediately taken to the prison hospital because he could not breathe properly."

Once the riot and blaze had been brought under control, the prison authorities launched an investigation in which four prisoners were reportedly tortured to death. Ninety-eight other prisoners were locked in a punishment cell block. Ko Bo Kyi, the joint secretary of AAPP and himself a former Insein prisoner, said: "The authorities are to blame for this situation. As soon as the storm hit, they should have moved the prisoners to safety."