"We have been receiving a stream of reports from independent sources alleging discriminatory and arbitrary responses by security forces, and even their instigation of and involvement in clashes," said Pillay, the UN High Commissioner for Human Rights, the BBC reported on Saturday, July 28.
"Reports indicate that the initial swift response of the authorities to the communal violence may have turned into a crackdown targeting Muslims, in particular members of the Rohingya community."
Sectarian violence plagued the western Arakan state last month after the killing of 10 Muslims in an attack by Buddhist vigilantes on their bus.
The attack came following the rape and killing of a Buddhist woman, for which Buddhists blame Muslims. The violence has left dozens of people dead and tens of thousands homeless. The official death toll of the rioting and its aftermath has been put at 78, although the real figure may be much higher.
Questioning the official death toll, Pillay welcomed a government decision to allow a UN envoy access to Rakhine state next week, but said it was "no substitute for a fully-fledged independent investigation".
Pillay's comments followed the announcement of the UN refugee agency (UNHCR) that about 80,000 people have been displaced following inter-communal violence in and around the towns of Sittwe and Maungdaw.
"Some displaced Muslims tell UNHCR staff they would also like to go home to resume work, but fear for their safety," spokesman Andrej Mahecic said. Thousands of Rohingya Muslims fled their homes after ethnic tensions rocked the western state of Arakan.