The United States has upgraded Japan to include it among countries it considers fully meet minimum standards for the elimination of human trafficking, according to a State Department report released Thursday.

It is the first time that the U.S. has ranked Japan on Tier 1, the highest classification on the four-tier list, a senior State Department official said, citing achievements Japan's government made during the reporting period that ended in March. The rankings in the list are Tier 1, Tier 2, Tier 2 Watch List and Tier 3.

Japan was upgraded from last year's Tier 2, partly due to the launch of an interagency task force to combat both enjo kōsai, or compensated dating, and the so-called JK business, which offers dating services by joshi kōsei, or female high school students, for adult men.