A main opposition leader in Mauritania and his key aides have been formally charged with plotting a coup in the run-up to this month's presidential election.

Early Tuesday in a speech marking the end of the Islamic holy month of Ramadan, Mauritanian President Maaouiya Ould Taya said the accused opposition leader, Mohamed Ould Haidallah, had been conspiring to destroy the state.

The comment came several hours after a spokesman for the Justice Ministry, Sall Moussa, read out the charges against Mr. Haidallah and 15 of his aides.

He says Mr. Haidallah, one of his sons and five members of his campaign team were charged with planning to overthrow the government. Eight other aides were indicted as accomplices in the alleged plot.

Mr. Moussa also said the government would not allow foreign lawyers to defend Mr. Haidallah. The head of a Senegalese-based group of lawyers trying to help Mr. Haidallah, Alioune Tin, says he fears there could be a social explosion because of this case in Mauritania.

"There is a great tension there and I think that there is a bomb," he said. "We do not wait until the bomb explodes, the social bomb, to get a conflict to come and to see how to put out the fire because in Africa often the elections very often we have conflict. We have conflict in Ivory Coast, Liberia, Madagascar and so on and we don't need now other conflicts in our sub-region in West Africa."

Mr. Haidallah is a former president who took power after a 1979 coup, and was himself overthrown by the current president, Mr. Taya, in a 1984 military coup. He came in second in the November 7 presidential election, and was arrested two days later.

One of Mr. Haidallah's few aides not in custody, Mohamed Ould Rashi, calls the prosecution a masquerade. He says the authorities never issued a warrant to search Mr. Haidallah's premises or arrest him. He says the trial, which is scheduled to begin December 1, will be a sham.

Mauritanian lawyers for the accused have not been allowed to meet with their clients since their arrest.

President Taya survived a coup attempt in June, but suspected coup leaders have been on the run since then.