President Barack Obama announced on Tuesday a new offensive against what he called the "modern slavery" of human trafficking.
Obama said 20 million people around the world, including some in the United States, are trapped by traffickers, whether as prostitutes or barely paid workers.
"It's a debasement of our common humanity," Obama said in a speech to the Clinton Global Initiative, a coalition of civil society groups, in New York. "I'm talking about the injustice, the outrage, of human trafficking, which must be called by its true name — modern slavery."
The president said he had ordered US agencies to ramp up efforts to eliminate human trafficking.
This will include tightening compliance with laws preventing federal contractors from using trafficked workers, strengthening legal procedures to combat traffickers and help victims, and publicising the problem.
"Our message today to them is, to the millions around the world, is we see you, we hear you," Obama said, addressing what he said were the often unseen victims of traffickers. "Our fight against human trafficking is one of the great human rights causes of our time."
Obama, America's first black president, called trafficking "barbaric" and said he did not use the word slavery lightly.
"When a man desperate for work finds himself... working for, toiling for, little or no pay and is beaten if he tries to escape, that is slavery," Obama said. "When a little boy is kidnapped, turned into a child soldier, forced to kill, or be killed, that is slavery."
Obama said America had long rejected slavery, but that "for all the progress that we've made, the bitter truth is that trafficking goes on right here in the United States".
He asked former victims turned advocates to stand up in the audience at the conference centre, calling them "an incredible inspiration".
"These women endured unspeakable horror, but in their unbreakable will, in their courage, in their resilience, they remind us that this cycle can be broken. Victims can be not only survivors, they can become leaders," Obama said, leading sustained applause for the women.