Lagos, Nigeria (CNN) Nigeria's anti-trafficking agency says it has received concrete intelligence that around 20,000 Nigerian girls have been forced into prostitution in Mali.

Many of the girls are working in hotels and nightclubs after being sold to prostitution rings by human traffickers, according to a fact-finding mission carried out by the agency in collaboration with Malian authorities in December.

NAPTIP's Arinze Osakwe told CNN most of the girls said they were lured by human traffickers who promised them employment in Malaysia.

"The new trend is that they told them they were taking them to Malaysia and they found themselves in Mali. They told them they would be working in five-star restaurants where they would be paid $700 per month," Osakwe, who was part of an earlier NAPTIP rescue mission, said.

Some of the girls had been sold as sex slaves in gold mining camps in northern parts of Mali, he said.

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