Mauritania and Haiti have the highest proportions of slaves in the world. Bruno Vincent/Getty

Slavery remains a serious global problem, with 29.6 million people in various states of forced servitude, including sexual exploitation, debt bondage and forced marriage, according to a new report.

Mauritania and Haiti have the highest proportions of slaves, while India, Pakistan and China have some of the highest absolute numbers, the Walk Free Foundation said in its first Global Slavery Index report, published Wednesday. The forms of bondage violate international decrees, including the 1926 Slavery Convention, an international treaty, and the UN Trafficking Protocol.

Native-born slaves are often found in poorer countries, while exploited workers from poorer parts of the world regularly end up in rich countries where they are often trafficked. In India, some native-born slaves never leave their own villages, Walk Free found.

"Today some people are still being born into hereditary slavery, a staggering but harsh reality, particularly in parts of West Africa and South Asia," the report states.

"Other victims are captured or kidnapped before being sold or kept for exploitation, whether through 'marriage,' unpaid labor on fishing boats, or as domestic workers," the report continues. "Others are tricked and lured into situations they cannot escape, with false promises of a good job or an education."

The 10 countries with the highest number of enslaved or exploited workers, according to Walk Free, are: India, China, Pakistan, Nigeria, Ethiopia, Russian Federation, Thailand, Democratic Republic of the Congo, Myanmar and Bangladesh.

But Mauritania, with about 150,000 slaves, retains the highest proportion of enslaved people in the world, with aspects of "chattel slavery" that harken back to the American experience of the institution, where human beings are considered "full property of their masters who exercise total ownership over them and their descendants."

Many slaves in the West African nation were born into classes that have toiled as slaves for generations.