The State Department says that up to 27 million people worldwide are trapped in some form of human trafficking and slavery.
The department's latest annual report revealed only 33 countries have complied with laws to end human trafficking.
Secretary of State Hillary Clinton unveiled the report Tuesday. She noted that other countries are making progress in fighting modern-day slavery, but said there's still lots more to be done -- even in the United States.
"This report gives a clear and honest assessment of where all of us stand," Clinton said. "It takes a hard look at every government in our world including our own...It is important that we hold ourselves to the same standard as everyone else."
Overall, the U.S. was ranked among the top countries combating human trafficking, but researchers said the nation needs to improve techniques for gathering data on the crime.
North Korea, Iran, Sudan, and the Democratic Republic of the Congo were ranked as some of the worse offenders.
The Polaris Project, a non-profit group fighting human trafficking, said calls reporting sex trade and modern-day slavery are on the rise.
The group received more than 19,000 calls in 2011 -- a 64 percent increase according to Polaris Project leaders.