"The sexist, insulting language used against the UN's independent human rights expert on Myanmar... Is utterly unacceptable," UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said in a statement here.
UN Special Rapporteur on Myanmar Yanghee Lee was in Myanmar last week to highlight the plight of the Rohingya Muslims.
During her visit, Buddhist nationalist monk Ashin Wirathu used abusive language against her.
"Don't assume you are a respectable person, just because you have a position in the UN...," the monk said, referring to Lee.
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"It is intolerable for UN Special Rapporteurs to be treated in this way and I call on religious and political leaders leaders in Myanmar to unequivocally condemn all forms of incitement to hatred including this abhorrent public personal attack against a UN-appointed expert," Al Hussein said.
In anti-Muslim riots in 2012, more than 200 people were killed in Myanmar.
Some 1,40,000 people, mainly Rohingya, live in miserable camps in Rakhine state following the 2012 clashes.
The UN recently passed a resolution, urging the Myanmar government to grant citizenship to the stateless Rohingya.
"Instead of attacking Lee personally, I invite community, religious and political leaders in Myanmar to tackle the substance of her concerns," Al Hussein said.
Myanmar government said it is investigating the speech made last Friday.