Geneva: The United Nations is getting daily reports of rapes and killings of the Rohingya minority in Myanmar and independent monitors are being barred from investigating.
UN human rights chief Zeid Ra'ad al-Hussein said in a statement that the government, led by Nobel Peace Prize-winner Aung San Suu Kyi, had taken a "short-sighted, counterproductive, even callous" approach to the crisis, risking grave long-term repercussions for the region.
Who are the Rohingya? - More than one million Rohingya Muslims live in Rakhine State in Myanmar but in apartheid-like conditions.
At least 86 people have been killed, according to state media, and the United Nations has estimated 27,000 members of the largely stateless Muslim Rohingya minority have fled across the border from Myanmar's Rakhine state into Bangladesh.
"The repeated dismissal of the claims of serious human rights violations as fabrications, coupled with the failure to allow our independent monitors access to the worst affected areas in northern Rakhine, is highly insulting to the victims and an abdication of the Government's obligations under international human rights law," Mr Zeid said in the statement.
"If the authorities have nothing to hide, then why is there such reluctance to grant us access? Given the continued failure to grant us access, we can only fear the worst."
UN human rights spokeswoman Ravina Shamdasani said the UN human rights office had submitted a formal request for access to the area, which had not yet been granted.
Adrian Edwards, a spokesman for the UN refugee agency UNHCR, said his colleagues in Bangladesh had spoken to more than 1,000 newly-arrived refugees in the past few weeks who gave accounts of houses being burned, targeting of civilians and traumatised women and children who had witnessed the killing of family members.
UNHCR could not verify the accounts first-hand, but Mr Edwards said the agency was was extremely concerned.
Mr Zeid said in June this year that crimes against humanity may have been committed and if the government did not handle the situation very carefully and address the grievances of the Rohingya minority, violence could ensue, Ms Shamdasani said.
"Unfortunately this is exactly what has happened in the past couple of months," she added. "We are worried that this is going to get further out of hand. This is perfect breeding ground for violent extremists."