Speaking to Anadolu Agency, Anita Schug said 102 Rohingya Muslim women and children have been held in Buthidaung prison since August 2017 over "false allegation."
She called on international community to pressure Myanmar authorities for the release of the prisoners.
About 120,000 Rohingya Muslims in Myanmar’s restive Rakhine State were subjected to forced starvation and violations by the authorities, Schug noted.
She said around 700 to 800 Rohingya prisoners in Saudi Arabia have also been awaiting their release for the last five years.
Since Aug. 25, 2017, some 750,000 Rohingya, mostly children and women, have fled to neighboring Bangladesh after Myanmar forces began a crackdown on the minority Muslim community, according to Amnesty International.
At least 9,400 Rohingya were killed in Myanmar's Rakhine State from Aug. 25 to Sept. 24, 2017, according to Doctors Without Borders.
In a report published last December, the global humanitarian group said the deaths of 71.7 percent or 6,700 Rohingya were caused by violence. They include 730 children below the age of 5.
The Rohingya, described by the UN as the world's most persecuted people, have faced heightened fears of attack since dozens were killed in communal violence in 2012.
The UN has documented mass gang rapes, killings -- including of infants and young children -- brutal beatings, and disappearances committed by security personnel.
In a report, UN investigators said such violations may have constituted crimes against humanity.