(Reuters) - A U.S. State Department report on human trafficking warned on Thursday that removing children from their families made them easy targets for traffickers, raising questions about the Trump administration’s policy of separating immigrant children and parents illegally crossing the U.S-Mexico border.

FILE PHOTO: People displaced by violence walk in the banks of Mayu river with their belongings while moving to another village, in Buthidaung in the north of Rakhine state, Myanmar September 13, 2017. Picture taken September 13, 2017. REUTERS/Stringer

The annual Trafficking in Persons report looked at 187 countries and territories and ranked them into four tiers. In a special section, the State Department said children should only be removed from their families as a “temporary, last resort.”

John Sifton, an advocacy director for Human Rights Watch, said the report “is an indictment of the Trump administration’s own policies with respect to asylum seekers and others seeking entry into the United States.”

Since April, more than 2,300 children have been separated from their parents as a result of U.S. President Donald Trump’s “zero-tolerance” policy for illegal immigrants. Children were kept in shelters while their parents waited to have their cases heard by a judge.

Faced with criticism at home and abroad, Trump signed an executive order on June 20 requiring families be detained together for the duration of legal proceedings, but many could remain apart as legal challenges drag on.

A senior State Department official said the United States has screening standards for trafficking indicators when children cross the border unaccompanied or are separated from their parents.

Trafficking indicators can include children who eat apart from family members, travel unaccompanied by adults and children who have no time for playing, according to the United Nations.

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The U.S. report downgraded Myanmar to its list of worst offenders, accusing the southeast Asian country of human trafficking and using child soldiers.

A Tier 1 ranking is for countries that meet minimum U.S. standards; Tier 2 for those making significant efforts to do so; Tier 2 Watch List for those meriting special scrutiny; and Tier 3 for countries that fail to fully comply with the minimum U.S. standards and are not making significant efforts to do so.

A Tier 3 ranking can trigger American sanctions limiting access to U.S. and international foreign assistance.

Gabon, Laos, Papua New Guinea and Bolivia were downgraded to Tier 3 from the Tier 2 Watch List in the report, which is intended to spur countries into curbing human trafficking.

“The world should know that we will not stop until human trafficking is a thing of the past,” Secretary of State Mike Pompeo said at a department event on Thursday where he and Trump’s daughter and adviser Ivanka Trump, honored “heroes” fighting human trafficking around the world.

Meanwhile, Sudan was upgraded to the second-to-worst ranking at a time of improved relations between the U.S. and Khartoum. The U.S. lifted some sanctions against Sudan in October and is considering easing more.

While the report is not meant to be influenced by geopolitical considerations, both the Trump and Obama administrations have been accused by human rights groups of prioritizing economic and security interests over human trafficking concerns.

A Reuters examination in 2015 found that U.S. diplomats pressured the office charged with grading global efforts for the report into inflating assessments of 14 strategically important countries. As a result, Malaysia, Cuba and China and countries such as India, Uzbekistan and Mexico, received better grades than the State Department’s human rights experts wanted to give them, the sources said.

Thailand and Pakistan were upgraded to Tier 2 this year, among a list of countries making significant efforts to comply. North Korea, China and Russia remained listed as some of the worst offenders. China was downgraded to Tier 3 last year.

Iran and Niger were added to the child soldiers list, while Sudan was removed. Those countries can be restricted in receiving U.S. military aid. Iraq and Myanmar were put back on the list after being removed last year.