One of the world's most secret execution rooms was opened up to reporters for the first time this weekend, the likely first step in a long-delayed debate on Japan' s controversial death penalty.

The Justice Minister, Keiko Chiba, who opposes the death penalty, ordered the ministry's conservative bureaucrats to allow the press to visit Tokyo Detention Centre to stimulate public debate on hanging.

A select group of reporters was allowed to take pictures of the execution chambers, including the room where prisoners are hanged.

Visitors have only been allowed to see the gallows on three occasions. In each case they were members of parliament who were forced to surrender recording and photographic equipment before their visit. What little is known about the centre comes mainly from former prison guards.

Last month, Chiba became the first justice minister to witness an execution when she sat grey-faced through the hangings of Kazuo Shinozawa, 59, and Hidenori Ogata, 33. The decision caught many people by surprise – Chiba was widely expected to begin a moratorium on the death penalty.

She said she hoped her actions would help the public decide on the system's merits. "It was the most open we could be, after considering the feelings of death row inmates, those who are close to them and prison guards as well as security problems."

Footage of the facility released by the state broadcaster NHK showed an anteroom with chairs, a large Buddhist altar and low table, where the execution order is read to the condemned. In a second room, a blue curtain conceals an observation chamber and a platform with a trapdoor marked in red. Some reporters said the entire facility was chilled by air-conditioners and smelled of incense.

Foreign reporters were banned from the tour, which did not show the hangman's noose or the area where the body is collected beneath the trapdoor.