Millions of men, women and children around the world were victims of modern slavery last year, according to a new U.S. report of human trafficking.

While data from the U.S. Department of State cataloguing the number of trafficking investigations, prosecutions, convictions and sentences have identified more than 42,000 victims worldwide, the International Labour Organization estimates that an even greater number — 20.9 million — are caught up in the modern slave trade at any time.

The annual Trafficking in Persons report, released by the State Department, sheds light on the dark underbelly of human trafficking, an umbrella term that includes sexual exploitation, child prostitution, forced labour and debt bondage. It can involve, but does not require, the movement of people from place to place.

"These victims of modern slavery are women and men, girls and boys, and their stories remind us of what kind of inhumane treatment we are still capable of as human beings," Secretary of State Hillary Rodham Clinton said. "Some are lured to another country with false promises of a good job or opportunities for their families. Others can be exploited right where they grew up, where they now live."

The report analyzed conditions in over 180 countries, including the United States, and ranked them according to their effectiveness at fighting human trafficking.

Seventeen in all were included in the worst-offending group of countries. These nations, down from 23 last year, do not reach minimum international standards to combat the practice and are not making any significant effort to do so.

Syria blacklisted

Syria was added to the list of worst offenders for the first time and could face sanctions from the U.S. government. According to the State Department, Syrian President Bashar al-Assad's regime fails to investigate and punish offences or offer protective services to victims.

More than 40 other nations were placed on a watch list that could lead to sanctions unless their records improve.

Regional figures, persons in forced labour (U.S. Department of State)

First-hand accounts from victims highlighted the physical and psychological toll of modern slavery.

“I wasn’t allowed to go anywhere, they locked us in. They didn’t lock us in the house, they locked us in our room. The three of us in a size of room that’s not enough for one person," recalls a labour trafficking survivor whom the report refers to as Todor. "I guess they rented us out, or landed us, or bought us? I don’t understand what happened. They simply [abused] us physically, mentally and emotionally during that eight months while I was there. I still am afraid, what will happen if they find me, or when they leave jail. I can’t go through that terror again, what I gone through while I was with them.”

The report encourages governments around the world to adopt laws and regulations that will enable them to identify and protect victims of human trafficking. It notes that the next few months will mark the 150th anniversary of the Emancipation Proclamation, a document ratifying U.S. President Abraham Lincoln's commitment to abolishing slavery.

“The problem of modern trafficking may be entrenched, and it may seem like there is no end in sight," writes Clinton. "But if we act on the laws that have been passed and the commitments that have been made, it is solvable.”

With files from The Associated Press