'I have never felt heat like that' - a survivor on watching 33 cellmates die in Nigeria

Usman Muhammad pauses by the entrance to a tiny Nigerian prison cell and leans his forehead against the wall unable to speak.

The day before he had been trapped inside the stifling room, measuring roughly 6m (19.7ft) by 3m (9.8ft), with more than 50 other prisoners.

Thirty-three of his cellmates died in the cramped conditions in the prison in Minna, the capital of Nigeria's Niger state - and four died later in hospital.

The mass deaths caused an outcry and sparked protests , including attacks on public buildings, as relatives and locals demanded answers.

Federal officials had initially blamed the deaths on a diphtheria outbreak but exactly what happened is now the subject of an investigation.

"I have never felt heat like that in my life. When we touched each other's bodies, it felt like fire burning," Muhammad tells the BBC once he is able to gather his thoughts.

When he was locked inside, there was standing room only amid humidity levels of more than 90%, which in some circumstances can be dangerous to human health as it prevents the natural cooling mechanism of sweat drying on the skin.

The temperature outside was above 25C and the only ventilation came from a small, high-up window.