GENEVA — Myanmar came under renewed international pressure on Tuesday for its treatment of Rohingya Muslims as United Nations officials said it should be investigated for crimes against humanity and possibly genocide by security forces.

The country’s security forces “deliberately and massively targeted civilians” in operations that drove more than 626,000 Rohingya, half the population of Rakhine State, into neighboring Bangladesh, Zeid Ra’ad al-Hussein, the United Nations high commissioner for human rights, told a special session of the Human Rights Council that convened in Geneva on Tuesday.

“Can anyone, can anyone, rule out that elements of genocide may be present?” Mr. al-Hussein, said, detailing “acts of appalling barbarity” committed by the security forces since August after decades of systematic discrimination and persecution.

The human rights chief had previously described Myanmar military operations in Rakhine as a textbook example of ethnic cleansing. His reference to genocide elevates the charge to the gravest of crimes against humanity: acts aimed at destroying in whole or in part a national, ethnic, racial or religious group.