Speaking to a conference of women activists in Reykjavik, Iceland, Mrs Clinton denounced a system that allows girls to be lured from home and "trafficked like drugs across state lines and sold into prostitution".

"We are working to stop trafficking of women and girls in this region and around the world," she said.

Mrs Clinton sees prostitution as a global problem

"No government and no citizen can rest until we stop this modern form of slavery, protect its victims and prosecute those who are responsible."

Mrs Clinton was addressing around 400 women delegates from the United States, Russia, the Baltic states and the Nordic region at the end of a week-long European tour.

The First Lady also praised the progress former communist states had made towards democracy over the past 10 years.

But she recognised that this had brought its own ills and said former Eastern-bloc countries would need more help to face hardships stemming from the transition.

A shopper rushes past as Mrs Clinton tours downtown Reykjavik

The speech was her most outspoken since the start of the tour, which also took in Slovakia, Poland and Spain.

Although she is almost certain to stand for the United States Senate in next year's elections, the White House said her trip was not linked to domestic US politics.

Mrs Clinton held up Iceland and the other Nordic states as models for women's equality. But she also acknowledged the pressures felt by women living in modern, developed democracies.

Problems with democracy

"Too many women are asking what good is democracy when we don't have affordable child care or health care. Too many workers are asking what good is a free market when we are the first to be fired and the last to be hired," she said.

But she made clear her view that the US government believed the causes of women and democracy were inseparable.

"Women's rights are human rights. The same rights which men have are rights which women must have, and deserve," she said.