Police find it hard to compete with international crime syndicates who rake in $870 billion a year via activities from drug trading and human trafficking to identity theft, a top UN official said Wednesday.

"This is an enormous amount of money," Yury Fedotov, head of the United Nations Office on Drugs and Crime, told AFP in an interview.

If crime syndicates were classed as an industry, their collective clout would rank them among the world's top economic players.

Crisis-era cuts have widened a longstanding financial gulf between criminal gangs and those who fight them, Fedotov said.

"Gangs are better funded than any law enforcement institution. That is clear, and especially if we compare the huge amount of illicit revenues with limited budgets of many law enforcement institutions," he said.

But funding is just part of the problem, Fedotov explained, as law enforcement agencies struggle to keep up with shape-shifting networks that move faster than the traditionalist mafias of the past.

"Contemporary organised crime is also sophisticated and highly adaptive," Fedotov said.

"We should be more flexible, and not only follow the flow, but also prevent and anticipate developments in terms of organised crime," he added.

Cybercrime is a major growth area, he explained, given that around one third of the world's population now has active access to the Internet.

The annual proceeds of online identity theft alone are estimated at $1.0 billion, he noted, though that is still outstripped by $20 billion generated by trafficking in endangered species.

In the narcotics trade, meanwhile, concerns focus on the rising number of designer drugs.

Fedotov also flagged worries about rising drug trafficking via the troubled Sahel and West Africa -- notably through lawless Guinea Bissau, which he dubbed the "weakest link".

The trade through the region has been stoked by notoriously violent central American cocaine-running gangs whose north American markets have shrunk.