Host countries are struggling to support the more than three million Syrian refugees that have been registered across the Middle East.
The number of Syrians who have fled their country has surpassed three million, the UN says, appealing for "massive" support to help host countries cope with the growing influx.
UN Refugee Agency (UNHCR) High Commissioner Antonio Guterres said that the agency had registered more than 3 million Syrian refugees across the Middle East, in addition to thousands more who have fled Syria and have gone unregistered.
"Without much more massive support, the international community cannot take for granted that the countries will be able to go on and accept hundreds of thousands or millions of Syrian refuges," Guterres added in the Jordanian capital Amman.
"This is the moment to preserve the asylum space in the region and much more massive support is required."
The donor-reliant UN agency has received 850 million dollars from the international community to extend assistance to Syrian refugees across the region. Jordan alone needs 1.8 billion dollars this year to assist the 600,000 refugees it hosts.
There have been reports that host countries have begun restricting entry to the estimated 7,000 Syrians fleeing their homeland each day.
Jordanian officials have refuted reports of border closures, saying that the country continues to receive more than 400 Syrian refugees daily.
Syria's crisis started in March 2011 with pro-democracy protests, which soon developed into a devastating war after al-Assad's regime attempted to quell the demonstrations.
The UN estimate that more than 100,000 people have been killed in the conflict.