Myanmar’s government is investigating a speech by a Buddhist monk in which he called a UN rapporteur a “whore”.
South Korean rapporteur Yanghee Lee was in Myanmar last week to highlight the plight of its Muslim minority.
But at a protest against the visit, monk Ashin Wirathu told Ms Lee she should have sex with Muslim Rohingya minority if she liked them so much.
The monk is a Buddhist nationalist who spent almost a decade in jail for inciting anti-Muslim violence.
Buddhist nationalism, largely led by monks including Wirathu, has been energised since the end of military rule in 2011.
In 2012, scores of people died and thousands were left homeless after violence broke out between Buddhists and Muslims in Rakhine state, mostly from the Rohingya minority. Violence has flared several times since then.
The UN says the Rohingya are being persecuted, and last week passed a resolution calling on Myanmar (also known as Burma) to give them citizenship.
But the Myanmar government views the Rohingya as foreign migrants, and there is widespread public hostility towards them.
During her visit, Ms Lee said Myanmar was in danger of slipping backwards in its transition to democracy since the end of military rule in 2011.