In one positive sign in the early afternoon, United Nations vehicles reached one of their destinations, the Damascus suburb of Moadamiya -- a place that the U.N. says it hasn't been able to resupply in about two years.
United Nations and Syrian Arab Red Crescent trucks also were headed to other Damascus suburbs -- including Madaya
, where until recently civilians made soups out of grass and leaves while dozens died of hunger -- as well towns near the northwestern city of Idlib.
The deliveries include high-energy foods like chickpeas and beans, tucked into packages that each can last a family of five for a month.
This is a bellwether moment for a deal, reached by diplomats last week in Munich, Germany
, that calls on Syrian government and rebel forces to pause their fighting, in part to allow aid to reach starving citizens after five years of bloodshed. The deal officially starts Friday, but Wednesday's convoys -- authorized by the Syrian government -- are an early measure of the fighters' willingness to abide by it.
"It's not important. It's essential, crucial," Staffan de Mistura, the U.N. secretary-general's special envoy for Syria, told CNN about Wednesday's convoys in an exclusive interview Friday in Damascus, Syria's capital.
More than 400,000 people are living in besieged areas in Syria
, he said.
"The people have been literally starving, and when they are not starving, they are very close to it," de Mistura said.
Starvation and bombs
Images of emaciated people in Madaya shocked the international community into action in January. Aid was delivered, but relief organizations believe there are more Madayas in Syria.
Making a cessation of hostilities work is a matter of trust, about building it in Syria and around the world, de Mistura said.
"This is a test. It is a test on what was decided in Munich. In Munich it was clearly a commitment by everyone to ensure this would be happening."
But initial hope formed at the negotiating table
began cracking not long after U.S. Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and other chief diplomats from around the world stood up from it Friday.
Two days after the deal, while diplomatic teams in Geneva, Switzerland, worked out finer points of the cessation, bombs pelted a Damascus suburb. And distrust simmered.
"We're very skeptical," a European diplomat said anonymously. "We've seen before with Russia that they tend to not necessarily respect this kind of agreement," he said.
On Monday, there were airstrikes on two hospitals and a school
, and accusations flew. Washington blamed the Syrian regime and Russia. Syria blamed one strike on the United States, which said it carried out no military operations in the areas attacked.
On Tuesday, the tone sharpened, when a U.S. State Department official said of Russia's stance on the fighting, "It's put up or shut up."
And Syrian President Bashar al-Assad
said "no one" was capable of making the fighting stop.
In the end, what matters is what happens starting Wednesday. De Mistura asks that all sides stop firing and let aid convoys get through.
Real success is measured in how many mouths they are able to feed.
"Are we able to actually reach as many people ... in the next few days, hours; at least six to seven locations, which include both besieged by the government and by the opposition?" he asked.
And it is measured in the peace people experience.
"The people are not besieged by weather, they're besieged by human beings that are fighting a horrible war," he said, "and therefore the cessation of hostilities is crucial."