An anti-slavery human rights activist in Niger has been charged with attempted fraud after his arrest.
Mr Weila is the head of Niger's anti-slavery organisation Timidria
Ilguilas Weila is accused of trying to falsely elicit money from foreign donors. He denies any wrongdoing.
The charges relate to a ceremony to free 7,000 slaves, cancelled at the last minute in March by the government who maintains slavery does not exist.
London-based Anti-Slavery International has urged the authorities to release Mr Weila and his colleagues immediately.
At least 43,000 people are thought to live in subjugation across Niger, which officially banned slavery in May 2003.
Mr Weila has been remanded in custody until a bail application is heard.
His lawyer told the BBC that charges of spreading false information had been dropped.
Four of his colleagues were set free on Wednesday.
The ceremony in March was due to be attended by representatives of the slaves, the government and human rights campaigners at In Ates, near the border with Mali.
A local chief had agreed to the release of the slaves, but authorities now say his letter to Timidria, Mr Weila's anti-slavery organisation, asking for financial aid to rehabilitate slaves was a forgery.
"There is not question of any attempt [by Timidria] to swindle money... We see this as another attempt by the government to clamp down on and muzzle Timidria," Romana Cacchioli, Timidria's Africa programme officer told Reuters news agency.
Mary Cunneen, director of Anti-Slavery International has condemned the arrest of Mr Weila.
"Slavery is a significant problem in Niger and we call on the government to work in co-operation with Timidria to achieve an end to this abuse," she said in a statement.
According to Timidria, males slaves are forced to work in farms and tender cattle, while women are confined to domestic duties.
The slave masters take the children from their mothers at two years old - to break the family bond as soon as the child is weaned. And so slavery is perpetuated from one generation to the next.
Anti-slavery International says President Mamadou Tandja is embarrassed by any talk of slavery at a time when he is head of the West African regional organisation - Ecowas
Acting under pressure, Niger's parliament made slavery punishable by up to 30 years in prison in 2003.