美国有线新闻 CNN 叙利亚军方宣布停火结束 联合国救援车队遭袭（在线收听）

We're getting started in the Middle East today with an update on what appears to be a crumbling situation in the nation of Syria.

"Just when we think it cannot get any worse, the power of depravity sinks lower." That's a quote from U.N. Secretary General Ban Ki-moon. He's referring to the apparent bombing of the United Nations' aid convoy, a group of vehicles that was reportedly trying to unload aid supplies in a town west of the Syria city of Aleppo.

The U.N. says 18 of the 31 trucks in the convoy were hit Monday night. A warehouse belonging to the Syrian Arab Red Crescent was also struck.

Twenty people were reportedly killed in the bombing.

No one has claimed responsibility for it and it's not clear yet whether the trucks and warehouse were shelled or hit by an airstrike. The bombing happened shortly after Syrian government officials declared that a ceasefire that took effect last week had ended.

The attack forced the United Nations to suspend sending aid convoys into the area around Aleppo, and that's a place that concerned humanitarian workers for months because an estimated 250,000 civilians are there in need of food, medicine and water. The dangers of reaching them mirror the complications of Syria's civil war.

CLARISSA WARD, CNN SENIOR INTERNATIONAL CORRESPONDENT: Well, if you take a look at a map, you get a much greater idea of the complexity of the situation. This is where that aid is needed the most, in eastern Aleppo.

This part of the city is controlled by the rebels. It's home to roughly 300,000 civilians and it's where the most intensive bombardment has been happening.

For months, it has been besieged by the regime of Bashar al-Assad. You can see regime territory is all of this area marked in red, entirely surrounding eastern Aleppo. That means there's no food or medical aid getting in.

When we visited Syria earlier this year, there was still one road into eastern Aleppo that was under the control of the rebels, Castello Road. It was very dangerous to travel because it's flanked by the Syrian army in red and by Kurdish fighters which you can see just there in blue.

Now, Castello Road is under the control of the regime. And this is the road that the aid trucks are hoping to take in. Several weeks ago, rebel forces were able to clear a small, shaky corridor down in this area called Ramouseh, but after heavy fighting, that area is now back under regime control, too.

So, in order to get aid trucks from the Turkish border into the hardest hit areas, they will need to go through regime, and rebel and Kurdish held areas. And negotiating that kind of access takes time.