Former president Jimmy Carter says in a new interview that the United States is the one of the world's worst offenders when it comes to modern-day slavery, saying its slave trade is worse today than it was even in the 1700s.

"The United States is one of the most culpable countries in ... modern slavery," Carter said in an interview on MSNBC's "Andrea Mitchell Reports." "The slave trade now greatly exceeds anything that happened in the 19th and 18th centuries."

The United States banned the importation of slaves starting in 1808, but slavery itself persisted for another half-century.

Carter said that, of the 29 million people living in bondage, 60,000 of them are in the United States. The former president said 200 young girls are sold into slavery every month in the city of Atlanta alone.

Carter is currently on a book tour. Part of the same interview aired Sunday on NBC's "Meet the Press."