Human rights groups have been lobbying for an international investigation over the past year, and they hope to persuade Japan to sponsor a resolution at the next session of the Human Rights Council in March that would create a commission of inquiry. Both the council and the United Nations General Assembly passed resolutions condemning North Korea in 2012 by consensus, unopposed even by China, the North’s closest ally.

Ms. Pillay expressed concern that international preoccupation with North Korea’s missile and nuclear weapons programs had diverted attention from human rights abuses that have “no parallel anywhere in the world.”

“What we are trying to do is put human rights as a priority in the international debate on North Korea,” said Juliette de Rivero, Geneva director of Human Rights Watch, one of more than 40 organizations in the International Coalition to Stop Crimes Against Humanity in North Korea that are backing the inquiry. “Right now it’s nearly invisible.”