Myanmar is seeking an ethnic cleansing of Muslim Rohingya minority from its territory, a senior UN official has told the BBC. Armed forces have been killing Rohingya in Rakhine state, forcing many to flee to neighbouring Bangladesh, says John McKissick of the UN refugee agency UNHCR.

Mynamar officials, however, say that Rohingyas are setting fire to their own houses in northern Rakhine state. All journalists and aid workers have been barred by the government from entering the region and the world doesn’t clearly know the extent of atrocities.

The Rohingyas, who number about one million, are seen by many of Myanmar’s Buddhist majority as illegal migrants from Bangladesh.

John McKissick said the Myanmar military and Border Guard Police had “engaged in collective punishment of the Rohingya minority” after nine border guards were killed on October 9 during an attack on border posts in Maungdaw. The government has blamed a Rohingya militant group for the act.

Security forces then sealed off access to Maungdaw district and launched a counter-insurgency operation. Soldiers have been accused of serious human rights abuses, including torture, rape and executions, which the government has flatly denied. It says militants have attacked helicopter gunships providing air support to troops.

Security forces have been “killing men, shooting them, slaughtering children, raping women, burning and looting houses, forcing these people to cross the river” into Bangladesh, McKissick said.

Earlier this week, Human Rights Watch had released satellite images which showed more than 1,000 homes had been razed in Rohingya villages over the past six weeks.

Myanmar held its first openly contested election in 25 years last November, with Nobel Laureate Aung San Suu Kyi’s National League for Democracy winning a landslide victory. Though she is barred from the presidency due to a constitutional rule, Suu Kyi, who serves as State Counsellor, is seen as de-facto leader.

But her government has faced international criticism over the dire situation in Rakhine state. Rights groups have questioned why journalists and aid workers are not being allowed to enter northern Rakhine.

More than 120,000 Rohingya Muslims are living in fetid camps in Rakhine State after violent clashes with their Buddhist neighbours in 2012. They have little access to health care and 30,000 of their children do not have proper schools, according to a UN report in June.

The report cited a “pattern of gross human rights violations” against the Rohingya, acts that it said could rise to the level of “crimes against humanity” in a court of law.