The deaths of three ethnic Rakhine men in Myanmar military custody and the secret cremation of their bodies has provoked outrage, as fears over military impunity increase in the intensifying conflict with Rakhine rebels.

A Myanmar court on Tuesday sentenced a prominent ethnic Rakhine leader to 20 years in jail for treason, a verdict likely to intensify anger amid fighting between the ethnic group and the army.

Panic is gripping thousands of Rohingya Muslim refugees living in no-man's land on the Myanmar-Bangladesh border, with daily clashes between Myanmar security forces and ethnic Rakhine insurgents.

The level of brutality used by Myanmar's military against the Rohingya minority is "hard to fathom", a UN investigator said Tuesday, presenting a damning report calling for top generals to be prosecuted for genocide.

A U.N. visit to Myanmar's conflict-battered Rakhine state was postponed Thursday, thwarting efforts to reach the epicenter of violence for the first time since the start of a massive exodus of minority Rohingya Muslims.

At least 18,500 Rohingya have crossed into Bangladesh since fighting erupted in Myanmar's neighboring Rakhine state six days ago, the International Organization for Migration said Wednesday.

Myanmar's Aung San Suu Kyi on Monday accused Rohingya fighters of burning down homes and using child soldiers during a recent surge in violence in troubled Rakhine state, allegations denied by the militants themselves.

Aung San Suu Kyi has denied security forces have carried out ethnic cleansing of Rohingya Muslims in Myanmar, speaking to the BBC after the UN rights council agreed to investigate allegations of rape, murder and torture against the army.

Three police officers were attacked with machetes in restive northwestern Myanmar on Saturday by assailants who were shot dead, the military has said, amid lethal violence that authorities have blamed on homegrown Islamist insurgents.

Peace talks between Myanmar's government and warring ethnic minorities kicked off Wednesday in a bid to end decades of conflict that have claimed thousands of lives and kept the country mired in poverty.