Myanmar's government imposed curfews and states of emergency last month in response to fighting between Buddhists and Muslims.
Police Lt. Col. Min Augn told The Irrawaddy, a Thai newspaper reporting on Myanmar, that his forces responded with rubber bullets "as a last resort" to stem the violence.
He said parts of the Mandalay district were relatively stable following weeks of violence. It was difficult controlling the violence because many Buddhists weren't discouraged by the police presence.
"Under such circumstances, we found it difficult to contain the situation if they happened to come forward," he said. "Another issue was the size of the crowd and the police forces ... there were more rioters than police."
Myanmar earned recognition for political reforms that began with general elections in 2010. Rights groups said the lingering violence may undo most of that progress, however.
U.N. special envoy on human rights Tomas Ojea Quintana said he had serious concerns about Myanmar's stability because it ignored "warning signs" from similar violence last year in Rakhine state.