The cuts, due to start later this year, could put further strains on the economy if they cause a big jump in inflation.

UNHCR spokesman Andrej Mahecic said many of the more than 1 million Afghan refugees in Iran's cities would be hit hard.

"While the government will provide a safety net of cash grants for Iranians, this will not be extended to refugees," he told a news briefing in Geneva.

Iran spends $100 billion a year — almost one third of gross domestic product — subsidizing essentials such as petrol, natural gas, electricity and food.

Last year official inflation was 11 percent, down from 25 percent the year before.

While nearly 2 million Afghans have returned home from neighboring Iran since 2002, many with UNHCR assistance, the UN agency said the pace of repatriation had slowed because of insecurity and poor economic conditions in Afghanistan.

It is now asking donor governments for additional funding to help provide basic care to those remaining in Iran.

"The figure of $18 million that we're requesting is to meet the anticipated gap in funding," he said.

The UNHCR's total programs for Afghan refugees in Iran are budgeted at $36.8 million for this year, but only one fifth of that sum has been received so far, Mahecic said.