The United States is looking at ways to stem the growing trade in sex slaves - an illegal market officials fear will overtake drug trafficking.

A State Department official told a senate hearing that international criminals were moving away from "guns and drugs" to marketing women.

Up to 2 million women world-wide are forced to work as prostitutes.

"There are weaker restraints and growing demand," Harold Koh, assistant secretary of state for human rights and labour, told a senate sub-committee on Near Eastern and South Asian affairs.

Each year, 50,000 women are taken to the US to work as sex slaves, officials said. Feeder countries include Ukraine, Albania, the Philippines, Thailand, Mexico and Nigeria.

Trafficking of women and children "may be the largest manifestation of slavery in the world today," said the panel chairman, Sam Brownback.

Enslaved

A 20-year-old Mexican woman told the hearing that her quest for a better life turned her into a sexual servant.

"I was enslaved for several months, other women were enslaved for up to a year," said Inez, a native of Veracruz who wore a disguise in case that traffickers retaliated against her family.

"We worked six days a week and 12-hour days," she said.

"We mostly had to serve 32 to 35 clients a day. Weekends were even worse."

Mr Brownback, of Kansas, spoke of meeting some women victims during an information-gathering trip to Asia in January.

"They are told they will be taking a job as a nanny and are given money," he said.

"Then they are taken across a border and held against their will."

Inez said men in Mexico promised her work at a restaurant, but then said she owed them a "smuggling fee" of $2,500 that she had to pay off by selling her body.

Law enforcement officials raided the brothel - but while some of the traffickers had been prosecuted, Inez said others escaped capture and returned to Mexico.

"They have even threatened to bring our younger sisters to the United States and force them to work in brothels as well."

Protection and prosecution

Bills aimed at curbing sex trafficking have been introduced in the House of Representatives and the Senate.

Officials urged senators to back efforts to curtail the trade with a three-pronged strategy of prevention, protection and assistance for victims, and prosecution of traffickers.

But they warned against using sanctions, warning that such measures would only worsen the economic conditions that made women vulnerable to sex traders.