"The situation is getting desperate," said the head of the UN refugee agency UNHCR, Filippo Grandi.
"We are already seeing children who aren't able to go to school, families who cannot access adequate shelter or provide for their basic needs," Grandi said.
As the civil war in Syria enters its seventh year, only $433 million of the $4.63 billion appealed for by the UN in 2017 had been received, the world body said.
The total was just 9 percent of what was needed for vital protection and assistance for Syrian refugees and host communities, the UN warned.
Throughout the region, water and sanitation services, employment and housing markets were all under strain, the UN said.
The war between rebels and forces loyal to Syria's President Bashar al-Assad has claimed over 320,000 lives.
"The conflict in Syria remains the largest humanitarian challenge in the world - with 13.5 million men, women and children inside Syria also in need of urgent assistance," the UN stated.
The warning came as a two-day international conference kicked off in Brussels aimed at hammering out a plan for Syria's future.
EU foreign affairs chief Federica Mogherini has billed the gathering as a follow-up to a donors' conference last year in London, which raised about $11 billion for humanitarian aid programmes in the war-wracked country.
But the Brussels meeting is likely to be overshadowed by the Trump administration's announcement last week that it would no longer focus on Assad's removal but on the wider war against terrorism, including the Islamic State jihadist group.
Asked what this meant for EU policy, Mogherini said she believed it "would be impossible" to return to the status quo in Syria.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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