Alex Neve of Amnesty International Canada said Aaron Yoon told him he was kicked, punched and hit with wooden sticks to the point of losing consciousness, Canada's Postmedia News reported.
"These torture sessions are all about getting statements wrung out of prisoners," Neve said.
The Canadian official was among representatives from Amnesty International who spent 10 days in the West African nation interviewing detainees.
They concluded that police in the country are using torture to coerce men, women and even children to confess to crimes while in custody.
Eleven children told the human rights delegation they had been tortured in police stations.
One teenage boy said police officers hung him upside down and beat him with their batons until he lost consciousness.