The U.N. refugee agency is alerting more than 33,000 vulnerable Iraqi refugees in Damascus through text messages on cell phones, which many of them use to keep in touch with family and friends.

The office of the U.N. High Commissioner for Refugees started a new food distribution program in Syria by sending 10,000 text messages to those eligible, U.N. deputy spokeswoman Marie Okabe said on Friday.

UNHCR has "found text messages to mobile phones are one of the most effective ways of communicating with the refugees, who often do not have a stable address but either they or someone close to them in their immediate community has a mobile phone," Okabe said.

More than 2 million people are displaced in Iraq, and a further 1.4 million are believed to be in Syria, which has kept its borders open to fleeing Iraqis. Jordan estimates it is hosting between 500,000 and 750,000 Iraqis.

About 4.2 million people have fled their homes in Iraq, where violence remains widespread more than four years after U.S.-led forces invaded the country and removed dictator Saddam Hussein.

The UNHCR has sought $223 million in aid to help distribute emergency supplies to the most needy of those displaced inside Iraq. It has also asked donors for funds to get an additional 150,000 Iraqi children into schools in neighboring countries where their families have sought refuge.