The Moroccan authorities have stepped in to block a conference being organised by a campaign group which alleges that the Spanish army used toxic gas to quell a Berber uprising in the 1920s.

The group, calling itself the Association for the Defence of Victims of the Rif War, says that more than 70 years on, the effects of the toxic gas are still being felt.

It says a conference to discuss the issue with international experts, due to take place at Al Hoceima in northern Morocco on 25 January, has been banned by the authorities, without explanation.

The Berber rebellion in the Rif mountains of northern Morocco is one of the most celebrated events in modern North African history.

Historical grievances

In July 1921, the Berber chieftan Abdulkrim gathered together a band of warriors armed with nothing but flintlock rifles.

They inflicted a humiliating defeat on the Spanish army - which at that time occupied northern Morocco.

Nearly half of the 26,000 soldiers were massacred and it took five years before the Spanish, reinforced by French troops, regained control.

Since Moroccan independence in the late 1950s, stories have emerged out of the Rif mountains about how Spain allegedly used German-manufactured toxic gas in their efforts to put down the Berber rebellion.

Berber campaigners say the details of this crime against humanity have been suppressed, not only by Spain but also the Moroccan monarchy, with which the Berber tribes in the Rif have separate historical grievances.

According to the Association for the Defence of Victims of the Rif War, many people in the mountains continue to die of cancer - more than 60 per cent of the total for the whole country - and they believe toxicity is to blame.

It is the second time in two years the group has been prevented from holding a conference on the issue.

The murky truth of the Rif war will apparently stay that way, at least for now.