Amnesty International claims that up to 1,000 people in Gambia have been kidnapped from their villages by witch doctors, taken to secret detention centres and forced to drink hallucinogenic concoctions.
Some have developed kidney problems and two have died after these attacks, the human rights group says.
Reports suggest that officials within Gambia including the police, army and the President's personal protection guards are accompanying witch doctors as they carry out their campaign.
Victims and their relatives told Amnesty International that witch doctors have visited villages with armed security and forcibly taken people they accused of being witches to secret detention centres. Many of those taken were elderly.
At the secret detention centres, where some have been held for up to five days, they are forced to drink unknown substances that cause them to hallucinate and behave erratically. Many are then forced to confess to being a witch. In some cases, they are also severely beaten, almost to the point of death.
Amnesty International UK Director Kate Allen commented: "These horrific attacks and kidnappings are part of a witch-hunting campaign that's spreading terror throughout the country. Already hundreds of Gambians have fled to neighbouring Senegal for safety after their villages were attacked."
Eyewitnesses and victims told Amnesty International that the witch doctors, who they say are from neighbouring Guinea, are accompanied by police, army and national intelligence agents. They are also accompanied by 'green boys' - Gambian President Yahya Jammeh's personal protection guards.
The most recent incident took place on 9 March 2009 in Sintet village in the Foni Jarrol district, where up to 300 people were forced to go to the President's farm in Kanilai.
According to one eyewitness: "At 5:00 am the paramilitary police armed with guns and shovels surrounded our village and threatened the villagers that anyone who tries to escape will be buried six feet under...Fear gripped the village...children were crying and traumatised. They randomly identified over 300 men and women who were forced at gunpoint into waiting buses and ferried to the President's hometown.
"Once there, they were stripped and forced to drink dirty water from herbs and were also bathed with these dirty herbs. A lot of these people who were forced to drink these poisonous herbs developed instant diarrhoea and vomiting whilst they lay helpless. I stayed there for five days. I experienced and witnessed such abuse and humiliation. I cannot believe that this type of treatment is taking place in Gambia. It is from the dark ages."
The incidents have taken place in the Foni Kansala district, an area near to President Jammeh's farm of Kanilai. However, many people are telling Amnesty International that the witch hunting campaign will spread throughout the rest of the country.
Witch doctors were invited to Gambia early in 2009, soon after the death of President Jammeh's aunt. The President reportedly believes that witchcraft was instrumental in her death.
Kate Allen continued: "The Gambian government has to put a stop to this campaign, investigate these attacks immediately and bring those responsible to justice."
On 8 March, Halifa Sallah, a prominent opposition figure who has written about the activities of the witch doctors for the main opposition newspaper, Foroyya, was arrested at his home. He has since been charged with sedition and spying, and is currently in Mile II, the Central Prison in the Gambia. His next court date is set for Wednesday 25 March.
Amnesty International is concerned that he is at risk of being tortured or ill-treated and that his trial will be unfair.