BEIRUT, Lebanon — A fierce winter storm that has unleashed barrages of rain and snow on parts of the Middle East this week has compounded the misery of the millions of Syrians displaced by their country’s civil war and left the organizations that seek to help them scrambling to keep up.

Frigid winds, driving rains and layers of snow have hit encampments in Syria’s neighboring countries, flooding settlements, collapsing tents and leaving refugees shivering in the cold and increasing the chances for illness, aid groups say. Three Syrians, including a child, were found dead in southern Lebanon after getting caught in a storm, Lebanon’s National News Agency reported.

“It is like the seven plagues of the Bible falling on these poor people,” said Jan Egeland, the secretary general of the Norwegian Refugee Council, which is helping displaced Syrians across the region.

Even before the storm gathered on Tuesday, nearly four years of war in Syria had created a staggering humanitarian crisis, with one-third of the country’s original 23 million inhabitants displaced and more than three million of those registered as refugees in other countries.