By Steve Schifferes BBC News Online in Washington

The victims are usually teenage girls

The US estimates that between 700,000 and 4m people each year are victims of human trafficking, one of the fastest growing crimes in the world.

The conference brings together for the first time local activists and justice department officials, parish priests and former victims, to discuss effective strategies to combat sex trafficking.

They are basically slaves .. it's a death sentence US Congressman Frank Wolf

The US State Department, which is sponsoring the conference, says the aim is to show activists that "they are not as alone as they thought, and that there are other people and other resources they can call on."

Among those who will be addressing the meeting are Sweden's Deputy Prime Minister, Margareta Winberg, the vice-president of Colombia, Francisco Santos Calderson, and John Ashcroft, the US Attorney General, who will speak on Tuesday.

Growing problem

Trafficking in human beings is now estimated to earn as much money for criminal syndicates as the global narcotics trade.

The collapse of the Soviet Union and the sharp rise in poverty in former Soviet republics, coupled with the opening of borders, has added to the problem in Europe.

Trafficking has also been on the rise in cultures where women have a lower social status.

According to Unicef's Kul Gautum, more than 30 million children have been traded over the last three decades in the Asia-Pacific region alone.

He said that teenage girls were lured abroad using "even more cruel and devious means than the original slave trade".

Anti-trafficking groups report that desperately poor parents are selling their daughters into the sex trade in some countries.

Taken away from their homes, across an international border, left with no other means of support, the victims of sex traffickers are kept as virtual prisoners and frequently physically abused.

And stamping out the sex trade has been hampered because in some countries, "the police, who are supposed to stop these crimes, are involved in crimes by offering protection to criminals," said Mr Gautum.

Concrete measures

John Miller, director of the State Department's Office to Monitor and Combat Trafficking in Persons, said that the US wanted concrete measures to tackle the problem both within countries and at the borders.

Within countries, better protection for rescued victims, tougher penalties against sex traffickers, and more effective education programs targeted at vulnerable groups, should have high priority.

But the US also wants "countries to focus on what they can do to increase the scrutiny of immigration officials at borders."

And Mr Miller added, it wants better collection and sharing of information.

US laws

In 2000 the US enacted laws to recognise that many women had been forced into prostitution, and to ensure that where trafficking rings are broken, they were treated as victims, not criminals.

The law provided funding to help victims recover from their ordeal as forced sex workers, including emergency medical treatment, food, shelter, and counselling services.

But according to Congressman Frank Wolf, one of the bill's sponsors, there is still a long way to go.

"They are basically slaves," he said. "With HIV/Aids, it's a death sentence."