Even before the first phase is completed, the fragile cease-fire agreement that has paused 15 months of war in Gaza between Israel and Hamas faces increasingly long odds of lasting or even reaching phase two.

Hundreds of truckloads of food, fuel and other supplies have arrived in Gaza each day since the cease-fire took effect. But the need is vast after 15 months of war.

Funding shortages may affect the U.N.'s ability to maintain aid flows at target levels throughout the Gaza ceasefire deal, a U.N. official told Reuters.

Since a six-week ceasefire between Israel and Palestinian militant organization Hamas came into force on Sunday, more and more aid has been reaching the Gaza Strip, according to the UN's Office for the Coordination of Humanitarian Affairs (OCHA).