Relief agencies struggling to reach hundreds of thousands of Rohingya Muslims displaced by strife in northwestern Myanmar are facing rising hostility from ethnic Rakhine Buddhists, who accuse the UN and foreign aid groups of only helping Muslims.
So far, the Myanmar government has only granted Red Cross organisations access to the area.
The United Nations suspended its activities and evacuated non-critical staff after the government suggested it had supported Rohingya insurgents.
Already battling against bad weather, tough terrain and obstructive bureaucracy, the Red Cross also ran into an angry mob, who believe the foreign aid agencies have ignored the suffering of Rakhine Buddhists in Myanmar's poorest state.
On Wednesday a mob in Sittwe, the capital of Rakhine State, tried to block a boat carrying International Committee of the Red Cross aid to the north, where attacks by Rohingya militants on August 25 prompted Myanmar's generals to order a sweeping counter-insurgency offensive.
The mob was armed with sticks, knives and petrol bombs, and only dispersed after police fired rubber bullets.
Four days earlier a Myanmar Red Cross truck was stopped and searched by Rakhine residents in Sittwe.
"With heightened tensions in Rakhine State, humanitarian staff and private contractors are facing serious challenges in implementing life-saving activities," said Pierre Peron, spokesman for the UN Office for the Coordination of Humanitarian Affairs in Myanmar.
In the past month, 420,000 Rohingya have fled into neighbouring Bangladesh to avoid what the UN human rights chief has called ethnic cleansing.
Foreign aid groups are now scaling up to help Bangladesh cope with a humanitarian disaster of biblical proportions.