The remote border region was plunged into crisis after Rohingya militants attacked police posts in late August, prompting a military backlash that has sent nearly a third of the Muslim minority population fleeing to Bangladesh.
Rohingya refugees fleeing the unrest have told stories of soldiers and Buddhist mobs burning entire villages to the ground, while the government blames militants for the arson.
On Monday the United Nations rights chief, Zeid Ra'ad Al Hussein, said the violence seemed to be a "textbook example of ethnic cleansing".
Hours after the warning, the Security Council announced it would meet Wednesday to discuss the crisis, which has heaped global opprobrium on Myanmar's civilian leader Aung San Suu Kyi.
A Nobel peace laureate, Suu Kyi has been pilloried by rights groups for failing to speak up for the maligned Rohingya minority, who are denied citizenship by the state and have suffered years of persecution in Buddhist-majority Myanmar.
Late Monday her office said Myanmar "welcomes the statements issued by the United Nations and a number of countries firmly condemning the terrorist attacks," without mentioning the UN's charge of ethnic cleansing.