Hundreds of thousands of people are trying to survive with the most basic resources as temperatures fall below freezing. Nearly five years of conflict have left much of the country's infrastructure destroyed or severely damaged.
"The humanitarian situation in Syria is catastrophic and deteriorating day by day. The people are facing a bitter winter ahead and they have very few resources. We need better access so that aid can be brought to the most vulnerable. The situation is nothing short of critical for many, many people," said Mr Mardini.
More than 12 million Syrians, including 5.5 million children, are in need of immediate humanitarian assistance. More than 4 million people have fled abroad and around 8 million are displaced within the country; many have been forced to move several times.
