Hailey said Myanmar officials recently announced that the government would deny visas to members of the UN Human Rights Council's fact-finding mission.
She stressed in a statement that "no one should face discrimination or violence because of their ethnic background or religious beliefs" and it's important that the government allow the mission to do its job.
The Rohingya face severe discrimination in Buddhist- majority Myanmar and were the targets of inter-communal violence in 2012 that killed hundreds and drove about 140,000 people from their homes to camps where most remain.