WASHINGTON — The Obama administration on Thursday listed Myanmar as among the worst offenders in human trafficking, consigning a country President Obama only four years ago brought in from the diplomatic cold to the same ranking as Iran, North Korea and Syria.

The designation, contained in the State Department’s annual Trafficking in Persons Report, came just weeks after the Treasury Department lifted a broad array of sanctions on Myanmar, including those applying to state-run banks and businesses. Senior officials argued then that although the country’s human rights record was not perfect, its leaders deserved to be rewarded for their steps toward democratization. Relaxing the sanctions, they said, would serve as an incentive for the government to further improve its behavior.

American officials said Myanmar had not met expectations for improvement, though they said its efforts had been “significant.” The determination could have potentially damaging effects on a relationship that was just showing signs of thaw.

The Obama administration re-established diplomatic ties with Myanmar in 2012, after a lengthy overture by Secretary of State Hillary Clinton to the country’s ruling generals, as well as to the pro-democracy leader Daw Aung San Suu Kyi.