The UN High Commissioner for Refugees, António Guterres, has described the conflict in Syria as "probably the most challenging humanitarian operation in decades".
Speaking at the launch of the UN's largest-ever aid appeal, he said he was concerned that the scale of the need in Syria was too large to be covered by the "traditional aid budgets of donor governments" alone.
The Syria conflict is, without a doubt, the one with the most dangerous regional and global impact on peace and security, and the worst humanitarian consequences, we have faced in a very long time ...
The amounts required are on a scale that is difficult to picture. As I have said many times before ... [it] is painfully clear that traditional aid budgets of donor governments will not be sufficient to cover the enormous needs generated by the Syrian crisis, and that support will have to come from broader funding mechanisms.
Half the population at the Zaatari refugee camp are children. After escaping violence at home they are now growing up on the edge of war.
In my second special report, I see how charities in Zaatari are working with Syrian children to try to numb the painful trauma of war.
Zataari, a Syrian camp for more than 100,000 refugees, is a place so desolate that only the truly desperate would call it home.