WASHINGTON - Prostitutes are usually termed sex workers by governments and social welfare groups to avoid demeaning them but the United States feels the switch unwittingly dignifies syndicates involved in the flesh trade.

The State Department's office combating human trafficking issued a directive Friday to US agencies urging them to avoid using terms "sex worker" or "child sex worker" and even advised governments not to use them.

"Of course, one can rationalize words such as 'sex worker' and "child sex worker" in an effort to avoid a demeaning label such as 'prostitute," said John Miller, the office's director.

"However, there are other substitutes such as 'women used in prostitution' or 'sexually exploited children' that are neither pejorative nor pretend that violence to women and children is 'work,'" said Miller, who retired Friday after campaigning extensively across the globe to stem the human trafficking problem.

During his four years on the job, the lanky former congressman has visited more than 50 countries and met more than 1,000 survivors of what he called "modern-day slavery."

Some 800,000 women, children and men are trafficked across national boundaries each year, most of whom are enslaved in the sex industry, the State Department says.

Human trafficking -- which refers to the transportation of persons for sexual exploitation, forced labour or other illicit activities -- threatens to stifle the livelihood of many Asian workers, the department warns.

Miller, who will take up a job as professor at the George Washington University, said language was an important tool in fighting human trafficking.

"In earlier centuries to avoid facing up to the suffering of slaves, words such as 'houseboy,' 'field hand,' and 'servant' were used.

"Today, words such as 'forced laborer,' 'sex worker,' 'child soldier,' and 'child sex worker' are comonly used," he said.

These words, he said, required scrutiny.

Laborers compelled to work on a plantation or in a factory may be "forced laborers" but they are also victims of slavery, he said.

Similarly, children kidnapped and forced to be killing machines can be termed "child soldiers" but are also casualties of slavery.

However, Miller said the most egregious use of language is "sex worker."

Many governments, non-governmental groups and even UN agencies term prostitutes as sex workers.

"People called 'sex workers' did not choose prostitution the way most of us choose work occupations," Miller said.

Clinical research, he said, showed that vast majorities of people in prostitution are subject to trauma, violence and rape, and 89 percent wanted to escape.

"These 89 percent are victims of slavery," he said.

As for children involved in the flesh trade, he said they could not be called "child sex workers" because they were not old enough to consent to or choose prostitition.

Children, many not even teenagers by some estimates, make up almost 50 percent of those in prostitution in the world, Miller said.

"What is occurring is the use of the language to justify modern-day slavery, to dignify the perpetrators and the industries who enslave," he said.

"Governments, non-governmental organizations and citizens who care about fighting human trafficking and want to break the cycle of stigmatization and victimization should not use words such as "sex worker" or "child sex worker.

"To abolish modern-day slavery we must not be afraid to call slavery by its real, despicable name," he said.