Human trafficking a $7 billion business

But global revenues were probably "significantly higher," Yury Fedotov, head of the Vienna-based UN Office on Drugs and Crime told journalists, calling for closer international cooperation to help quash smuggling networks, according to Agence France-Presse.

"Terrible tragedies are occurring daily as vulnerable women, children and men, place their trust in criminals to smuggle them across national borders," he said.

Only joint international efforts can help "prevent the smugglers from staying one step ahead of law enforcement," he continued.

The International Organisation for Migration estimates some 40,000 migrants have died since 2000 trying to make their way illegally to a new country, with 3,000 perishing while trying to cross the Mediterranean in 2014 alone.

Last month, as many as 500 migrants drowned in what the IOM called "the worst shipwreck in years," after traffickers reportedly rammed and sank the boat.