International aid groups in Burma have urged the government to allow free access to Arakan State, where an army offensive has sent 480,000 people fleeing to Bangladesh but hundreds of thousands remain cut off from food, shelter and medical care.

The latest army campaign in the western state was launched in response to attacks by Rohingya Muslim insurgents on security posts near the Bangladesh border on 25 August.

The government has stopped international non-government groups (INGOs), as well as UN agencies, from working in the north of the state, citing insecurity.

“INGOs in Myanmar are increasingly concerned about severe restrictions on humanitarian access and impediments to the delivery of critically needed humanitarian assistance throughout Rakhine [Arakan] State,” aid groups said in a statement late on Wednesday.

An unknown number of people are internally displaced, while hundreds of thousands lack food, shelter and medical services, said the groups, which include Care International, Oxfam and Save the Children.

“We urge the government and authorities of Myanmar to ensure that all people in need in Rakhine State have full, free and unimpeded access to life-saving humanitarian assistance.”

The government has put the Myanmar Red Cross in charge of aid to the state, with the help of the International Committee of the Red Cross. But the groups said they feared insufficient aid was getting through given the “enormous” needs.

Relations between the government and aid agencies had been difficult for months, with some officials accusing groups of helping the insurgents.

Aid groups dismissed the accusations, which they said had inflamed anger toward them among Buddhists in the communally divided state.

The groups said threats, allegations and misinformation had led to “genuine fears” among aid workers, and they called for an end to “misinformation and unfounded accusations” and for the government to ensure safety.

The United Nations has accused the army of ethnic cleansing to push Rohingya Muslims out of Burma, and rights groups have said the army has committed crimes against humanity and called for sanctions, in particular an arms embargo.

The United States said the army response to the insurgent attacks was “disproportionate” and the crisis raised questions about Burma’s transition to democracy after decades of military rule.

British Minister of State for Asia and the Pacific Mark Field described the situation as “an unacceptable tragedy” after visiting Burma and meeting leaders including Nobel laureate Aung San Suu Kyi.

“Burma has taken great strides forward in recent years. But the ongoing violence and humanitarian crisis in Rakhine risks derailing that,” Field said in a statement.

Britain, like other members of the international community, called for the violence to stop and humanitarian access to the area and for refugees to be allowed to return safely.

Suu Kyi has faced scathing criticism and calls for her Nobel Peace Prize to be withdrawn. She denounced rights abuses in an address last week and expressed concern about the suffering.

She also said any refugees verified as coming from Burma would be allowed to return.

Burma is getting ready to “verify” refugees who want to return, the government minister charged with putting into effect recommendations to solve problems in Arakan State said.

Burma would conduct a “national verification process” at two points on its border with Bangladesh under terms agreed during a repatriation effort in 1993, state media quoted Win Myat Aye, the minister for social welfare, relief and resettlement, as saying.

“After the verification process, the refugees will be settled in Dargyizar village,” the minister said, referring to a Rohingya village that was razed after 25 August, according to satellite imagery.

It is unclear how many refugees would be willing to return.

Previous government efforts to verify the status of Muslims in Arakan State were broadly rejected as under the process, Muslims would not be recognised as Rohingya, an ethnic identity they prefer but which Burma does not recognise.

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Most Rohingya are stateless and regarded as illegal immigrants from Bangladesh.

“As we’re Muslim, the government hates us. They don’t want our Rohingya community,” said refugee Zafar Alam, 55, sheltering from the rain under an umbrella near the Balukhali settlement in Bangladesh.

“I don’t think I’d be safe there. There’s no justice.”

The government would take control of fire-gutted land, Win Myat Aye said this week. Rights groups say about half of more than 400 Rohingya villages were torched.

Officials have announced plans for resettlement camps for the displaced, while UN officials and diplomats are urging the government to let people rebuild homes.