The U.N. estimates that more than 4 million Syrians have fled the country since the start of the civil war there four years ago, making it the worst refugee crisis in a quarter century.
The UNHCR says the total number of refugees that have left Syria could be more than 4.25 million by the end of the year. An additional 7.6 million people are internally displaced.
"This is the biggest refugee population from a single conflict in a generation," U.N. High Commissioner for Refugees António Guterres says in a statement. "It is a population that deserves the support of the world but is instead living in dire conditions and sinking deeper into abject poverty."
As The Associated Press notes: "The new figure shows that the flow of refugees is accelerating only 10 months after the agency recorded more than 3 million Syrians fleeing their country."
About 45 percent of the refugees are living in Turkey and most of the rest are scattered in four other countries: Lebanon, Jordan, Iraq and Egypt.
"Worsening conditions are driving growing numbers towards Europe and further afield, but the overwhelming majority remain in the region," Guterres added. "We cannot afford to let them and the communities hosting them slide further into desperation."
"UNHCR's appeal for $5.5 billion to support the Syrian refugees in 2015 is only 24 percent funded. The U.N. World Food Programme has already cut rations for refugees because of a lack of cash.
"About 86 percent of the 630,000 in Jordan live below the poverty line of $3.2 per day, the UNHCR statement said, while more than half of the 1.173 million Syrians in Lebanon live in sub-standard shelters."