Most nations reported some form of "modern slavery" last year involving mainly sex trade or forced labour, and women played a surprisingly big role in running the illicit operations, the UN has reported.

A global report released on Thursday found that although women and girls suffer most from sexual abuse, women accounted for the majority of traffickers in almost a third of the 155 nations the UN surveyed. Women also accounted for more than 60 percent of the human trafficking convictions in Eastern Europe and Central Asia, the study found.

About 20 percent of victims globally were children, mainly in Southeast Asia's Mekong region and parts of Africa.

"Women commit crimes against women, and in many cases the victims become the perpetrators," Antonio Maria Costa, director of the Vienna-based UN Office on Drugs and Crime, said in an interview.

"They become the matrons of the business and they make money. It's like a drug addiction."

The report by Costa's office was based largely on human trafficking convictions reported to the UN between September 2007 and July 2008.

About four of every five reported cases involved sexual exploitation; most of the remaining cases involved forced labor.

About 22,500 victims were rescued during that time.

But Costa's agency provided no overall figures for how many millions of people might be victimized.

"We only see the monster's tail," he said.

"How many hundreds of thousands of victims are slaving away in sweat shops, fields, mines, factories, or trapped in domestic servitude? Their numbers will surely swell as the economic crisis deepens the pool of potential victims."

Costa, who serves as the UN's chief crime fighter, said it's often difficult to get nations to address human trafficking because "it's at the crossroads" of other complex issues such as migration and prostitution.

Two of every five countries covered in the report had not recorded a single conviction from 2007 to 2008.

"Either these countries are blind to the problem or they are ill-equipped to deal with it," Costa said.

Sixty-three percent of the nations in the report had adopted some laws against human trafficking.

The UN said most did so only after its protocol against human trafficking entered into force in December 2003.

Coinciding with the report's release was the appointment of Academy Award-winning actress Mira Sorvino as a UN goodwill ambassador to help Costa's office fight human trafficking.