Speaking to a human rights council session in Geneva, the High Commissioner for Human Rights, Zeid Ra'ad Al Hussein, detailed the events in Myanmar's northwestern Rakhine state over the last few months.
The United Nations defines genocide as acts meant to destroy a national, ethnic, racial or religious group in whole or in part.
More than 600,000 Rohingya fled to Bangladesh after the Myanmar security forces launched a brutal offensive targeting the minority in the Rakhine state in late August.
Bangladesh and Myanmar agreed on November 23 to start the return of Rohingya within two months.
"Given all of this, can anyone rule out that elements of genocide may be present?"
Up until this point, United Nations officials have described the crisis as "ethnic cleansing" but the term genocide would increase pressure on officials in Myanmar. Bangladesh now hosts about one million Rohingya.
While conditions for the Rohingya are terrible, IOM spokesman Joel Millman says this huge refugee influx into Cox's Bazar is having a severe impact on the impoverished host communities in the region.
Crimes included "rape, gang rape by multiple soldiers, forced public nudity and humiliation, and sexual slavery in military captivity", Patten said.
Meanwhile, another Myanmar official has reportedly denied plans to hold any returning Rohingya in camps, following earlier reports that authorities were building large detention facilities for them. Its envoy Htin, referring to the accounts, said: "People will say what they wanted to believe and sometimes they will say what they were told to say".