The United Nations’ humanitarian programs to provide aid to millions of Syrian refugees are facing a “staggering” shortfall of nearly $3.5 billion, the U.N. refugee agency (UNHCR) warned, in a report released Thursday. According to the report, of the $4.5 billion needed for the programs to be implemented, just over $1 billion has been received so far.

“This massive crisis requires far more solidarity and responsibility-sharing from the international community than what we have seen so far,” António Guterres, the U.N. high commissioner for refugees said. “But instead, we are so dangerously low on funding that we risk not being able to meet even the most basic survival needs of millions of people over the coming six months.”

The Syrian civil war, which began in 2011 and has only become more violent since the rise of the Islamic State group last year, has so far claimed -- according to some estimates -- over 320,000 lives. Nearly 4 million people have been forced to flee the country, a vast majority of whom are now living in Turkey and Lebanon.

The huge funding gap has led to a reduction in the food assistance program for nearly 1.6 million refugees, the U.N. agency said, in a statement. Additionally, nearly 750,000 children have been unable to attend school and life-saving healthcare services are becoming too expensive for many of the impoverished refugees.

“Without urgently needed funds, the delivery of water and waste water services for millions of people across the region will also be in jeopardy. Up to 1.7 million people may face winter this year without fuel, shelter, insulation, blankets or warm clothes,” the U.N. refugee agency said, in the report co-authored by 200 agencies that are part of the Regional Refugee & Resilience Plan (3RP) to rehabilitate Syrian refugees.

Also on Thursday, the U.S. announced over $360 million in funds for those affected by the Syrian war, bringing the total humanitarian assistance provided by the U.S. in response to the conflict to over $4 billion since 2011, according to a state department press release.

“Unfortunately, even with the contribution we are announcing today, the UN appeal remains severely unfunded. The suffering and the needs of the Syrian people continue to mount to levels once unthinkable,” the state department said. “The United States recognizes that, along with emergency relief, we must address the long-term development needs of Syria’s neighbors -- shoring up health care and education systems, and economies overwhelmed by the millions of Syrian refugees.”