South American drug cartels have started to use West Africa as a hub for smuggling operations, UN experts say.
Most of the drugs coming via West Africa are destined for Europe
The head of the UN Office on Drugs and Crime in West and Central Africa told the BBC that some 40 tonnes of cocaine had recently been seized in the region.
Antonio Mazzitelli said lax policing in some West African nations was the main attraction for traffickers.
He said cartels mostly targeted Europe, but some drugs were being turned into crack for local consumption.
"It is a trend that we have already noticed in the last 24 months," Mr Mazzitelli told the BBC's World Today programme.
"They [the cartels] have already moved into West Africa," he said.
"In the last 18 months alone, recorded seizures in the Atlantic Ocean for cocaine - mostly in ships coming from West Africa - account for something in the range of 40 tonnes."
The UNODC chief said that logistically the region was a very "attractive transit point" for major cartels.
"Drug traffickers realise that if they ship drugs directly from Latin America on ships... towards Europe they risk seizures".
"So they prefer to unload their shipments somewhere on the midway and load it on other ships that are coming from non-suspicious locations like West African ports," Mr Mazzitelli said.