Iran hosts the largest number of refugees in the world and has a significant migrant population, including 4.5 million Afghans, according to Tehran, and, according to the UN, hundreds of thousands of Iraqis.

"With the recent escalation of conflict, refugees, other Afghans and host communities in Iran are struggling with concerns for their safety, job losses, psychological distress and urgent shelter needs," said Babar Baloch, spokesman for UNHCR, the UN refugee agency.

UNHCR and its humanitarian partners have put together a flash refugee response plan, urgently seeking $80 million to respond to the immediate humanitarian needs from March to May.

"This will cover 1.8 million Afghan refugees and Afghans under other status living in Iran, plus also a million in their hosting communities who have also been affected," Baloch told a press conference.

"In Iran, most Afghan refugees, they live with the urban communities side by side, and everyone is affected," he said, adding that UNHCR was getting "thousands of desperate calls every day" from Afghans seeking support.

The Middle East war erupted on February 28 when Washington and Israel launched strikes on Iran, with Tehran in turn attacking targets in Israel and Gulf nations.

The UN's International Organization for Migration said no atypical outflows of people from Iran had been detected.

Meanwhile, the International Committee of the Red Cross said the month of war had upended the lives of millions and sent shockwaves far beyond the region at a speed "that threatens to overwhelm the humanitarian response".

"Essential infrastructure critical for the supply of energy, water and health care has been damaged or destroyed. The use of heavy explosive weapons with wide area impact in urban settings has caused suffering and fear," the ICRC said in a statement.

"Without respect for the rules of war, civilians will continue to suffer profound consequences that could outlast the current conflict."