UN human rights experts have called on Burma to investigate allegations that security forces have killed unarmed civilians, burned villages and made arbitrary arrests in a Muslim-majority region where a crackdown has followed attacks on border police.

Aid agencies say up to 15,000 people, believed to be mostly Rohingya Muslims, have been displaced since armed men launched coordinated attacks on three posts along the northwestern border with Bangladesh on 9 October.

The government, which is led by Nobel Peace Prize winner Aung San Suu Kyi, has characterised the response of security forces as a carefully targeted sweep of northern Arakan State’s Maungdaw Township in search of the perpetrators.

Officials say security forces have killed 30 “attackers” and detained 53 suspects while searching for 400 suspected Rohingya militants, who seized dozens of weapons from border police.

Rights group and sources from the mostly stateless Rohingya group have told Reuters that civilians are bearing the brunt of the military-led operation. They say the death toll from the violence is higher than reported.

The UN envoy on human rights in Burma, Yanghee Lee, said she had received “repeated allegations of arbitrary arrests as well as extrajudicial killings occurring within the context of the security operations conducted by the authorities in search of the alleged attackers.”

“What troubles me most is the lack of access for a proper assessment of the true picture of the situation there at the present moment,” Lee said in a statement from Geneva on Monday.

“The blanket security operations have restricted access for humanitarian actors with concerning consequences for communities’ ability to secure food and conduct livelihood activities,” Lee added.

The United Nation’s special envoys on summary executions, internally displaced persons, and torture also joined Lee’s call for “proper and thorough investigations of alleged violations.”

Rohingya community leaders and local residents told Reuters on Monday that hundreds of people had been hiding out in rice paddies near their village since soldiers allegedly ordered about 2,000 people to leave their homes on Sunday.

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According to the UN Office for the Coordination of Humanitarian Affairs (UNOCHA), aid agencies still have no access to the 10,000 to 15,000 people thought to have been displaced from their villages by the latest violence in Arakan State.

An additional 3,000 people from the ethnic Arakanese Buddhist community have fled to monasteries, schools and camps, the agency said in an update Monday.

Food aid is not reaching 50,000 “food-insecure people” and 65,000 school children in Maungdaw Township who normally receive World Food Programme assistance, said UNOCHA.