Relief and Refugee Repatriation Commissioner Mohammad Abul Kalam has said Bangladesh and Myanmar have not yet started the Rohingya repatriation process.
The UN chief said the assaults were allegedly perpetrated by the Myanmar Armed Forces, known as the Tatmadaw, "at times acting in concert with local militias, in the course of military "clearance" operations in October 2016 and August 2017".
It comes despite warnings from the United Nations that Myanmar is not ready for their return.
Boats with Rohingya from parts of Rakhine state have continued leaving Myanmar in recent months.
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The Myanmar government announced in a Facebook post on Saturday that a family of five had returned to the country from the border area between Bangladesh and Myanmar, where thousands of refugees are holed up.
A member of a Rohingya family is issued with her ID card.
"The five members of a family came back to Taungpyoletwei town repatriation camp in Rakhine state this morning", according to the governments Information Committee.
Burma has strongly denied that allegation - saying the army had waged a legitimate operation against insurgent Rohingya militants who had attacked more than two dozen police posts and an army base in August.
Photos posted alongside the statement showed one man, two women, a young girl and a boy receiving the ID cards and getting health checks.
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"I hope, Myanmar will repatriate all the families within the possible shortest time", the home minister said.
Andrea Giorgetta from the International Federation for Human Rights (FIDH) criticised the repatriation announcement as "a public relations exercise in an attempt to deflect attention from the need for accountability for crimes committed in Rakhine state".
A Rohingya community leader confirmed to AFP news agency the return of the family.
On Friday, UNHCR said that the "conditions in Myanmar are not yet conducive for returns to be safe, dignified and sustainable", adding that "the responsibility for creating such conditions remains with the Myanmar authorities, and these must go beyond the preparation of physical infrastructure to facilitate logistical arrangements". Many refuse to return without a guarantee of basic rights and citizenship.
Although the Rohingya have lived in Burma for many generations, most Burmese consider them unwanted immigrants from neighboring Bangladesh and refer to them as "Bengalis", a term the Rohingya consider derogatory.
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