United Nations efforts to send food to 700,000 Afghans gathered near Iran are being frustrated by Afghan lorry drivers, who have hidden vehicles for fear of American attacks, a senior UN official said.
Marius de Gaay Fortman, the World Food Programme (WFP) representative in Iran, said stocks of food in the Taleban-controlled city of Herat were expected to run out this week.
Unless more can be sent quickly, the UN and Iran fear an exodus of refugees towards the nearby border.
Long before the attacks on America, the WFP was supplying nearly 8000 tonnes of food a month to Afghans driven to Herat by civil war and a severe drought.
Many Afghans living near Herat are ethnic Tajiks, who prefer Iran as a safe haven.