Six workers die in Italian tank

Investigators are hoping to work out what caused the accident

Six people have died while working inside a water purification tank on the Italian island of Sicily.

Officials in the town of Mineo are investigating the cause of the accident, which occurred on Wednesday.

News reports said there were two initial theories - that the workers may have been killed by chemical fumes, or by an electric shock.

Italian President Giorgio Napolitano decried the deaths and urged stricter enforcement of safety rules.

The number of accidents in the workplace has become a major political issue in Italy.

Fatal incidents have been called "white deaths".

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According to research institute Eurispes, an average of 1,376 people die each year in industrial or workplace accidents in Italy.

In March, four men died when they inhaled toxic sulphur fumes in southern Italy.

Campaigners say companies often do not enforce regulations, and employees often work without basic safety equipment like helmets, goggles and face masks.

It is thought the use of black market labour may also contribute to the number of accidents.