The exodus created by the four-year-long Syrian civil war now has become the U.N. refugee agency's largest crisis in nearly a quarter-century and risks deteriorating further as fighting shows no sign of ending. The Office of the U.N. High Commissioner for Refugees (UNHCR) confirmed Thursday that more than 4 million Syrian refugees have fled the country since hostilities started in March 2011. "This is the biggest refugee population from a single conflict in a generation," said U.N. High Commissioner for Refugees Antonio Guterres. "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 it reaches the mid-point of its fifth year, the Syrian civil war has generated a steady flow of refugees into neighboring countries such as Lebanon, Turkey, Iraq, and Jordan, burdening those countries' infrastructures and leading to overcrowded settlements where many refugees struggle amid high unemployment and minimal public services. Turkey alone hosts 1.8 million registered Syrian refugees. "Worsening conditions are driving growing numbers towards Europe and further afield, but the overwhelming majority remain in the region," Guterres said. "We cannot afford to let them and the communities hosting them slide further into desperation." While the war continues to push Syrians to flee to other countries, the conditions of those tapped inside the country's besieged cities remains dire. The U.N. Office for the Coordination of Humanitarian Affairs (OCHA) has warned that 12 million people in Syria remain in need of humanitarian assistance—a twelve-fold increase since 2011. More than 7.5 million people have been displaced by the conflict and another 4.8 million people are in need of humanitarian aid in difficult-to-reach and besieged locations.