Forty-five managers and employees of a mine in western Turkey have gone on trial accused of causing the deaths of 301 miners who perished in a fire last year in Turkey's worst mining disaster.

The defendants include the CEO and the general manager of mine company Soma Komur Isletmeleri A.S.. They did not attend the opening of the trial on Monday, over security concerns.

Human Rights Watch has welcomed the trial as a step toward justice for the victims but has also called for an investigation into state officials for failing to oversee safety measures.

Inspection reports said the coal had been smoldering for days before the May 13 disaster, releasing toxic gases.

Survivors have complained of poor conditions inside the mine, including a lack of gas masks.