Half a million Rohingya Muslims have been forced to flee Myanmar to escape violence, prompting the United Nations Security Council to hold its first public meeting on the escalating situation in more than eight years.
Aid groups in Myanmar have urged the government to allow free access to Rakhine State, where an army offensive has sent 480,000 people fleeing across the border to Bangladesh, but hundreds of thousands remain cut off from food, shelter and medical care.
Secretary-General Antonio Guterres urged the Security Council to take strong action, calling on authorities to halt military operations and allow aid access in the worst-hit areas.
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 August 25.
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 State," aid groups said in a statement.
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 Sate 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 aid getting through would "not be sufficient to meet the enormous humanitarian 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 towards aid workers 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 aid workers' safety.