Myanmar has told the UN independent investigator into human rights in the country that it will not cooperate with her or grant her access to the country for the rest of her tenure.
Yanghee Lee, UN special rapporteur, said she had been due to visit in January to assess human rights across Myanmar, including abuses against Rohingya Muslims in Rakhine State.
"This declaration of non-cooperation with my mandate can only be viewed as a strong indication that there must be something terribly awful happening in Rakhine, as well as in the rest of the country," she said in a statement on Wednesday.
Turkey's Prime Minister on Wednesday dubbed the killing of minority Muslim Rohingyas in Myanmar by its security forces "genocide" and urged the international community to ensure their safety back home.
Nobel peace laureate Aung San Suu Kyi's less than two-year old civilian government has faced heavy international criticism for its response to the crisis, though it has no control over the generals it has to share power with under Myanmar's transition after decades of military rule.
More than 650,000 Rohingya have fled into Bangladesh since August 25, when attacks by Muslim insurgents on the Myanmar security forces triggered a response by the army and Buddhist vigilantes.