Sallah, 56, is leader of the main opposition National Alliance for Democracy and Development in the tiny West African state which has been strongly criticised over its human rights record.

Magistrate Olagbutu Kayode told Sallah he had been charged with spying, illegal assembly and intended sedition.

Sallah, who was arrested on Monday, was immediately remanded in custody when he could not make the bail of one million dalasis, equivalent to around 30,000 euros.

Gambia, the smallest country on the African mainland, has been ruled by President Yahya Jammeh since he grabbed power in a bloodless coup in 1994.

Sallah is one of the government's most outspoken critics who has been arrested on a number of occasions in the past. He stood against Jammeh in the last presidential elections in 2006 which were won comfortably by the incumbent.

Members of his six-party coalition said his latest arrest was "politically motivated" and have demanded his immediate release.

Jammeh's regime has progressively toughened its response towards all forms of opposition.

Several journalists have been arrested and charged in recent months and two British missionaries are serving hard labour sentences for criticising the president.

A November report by Amnesty International said Jammeh's opponents are subjected to daily rights violations including torture and unlawful arrests. It also detailed a crackdown by authorities on the media.

Jammeh, a former wrestler, has brushed off criticism, saying in an independence day address last month that the west African country "has earned the respect and admiration of the world."