Syrian rebels fear huge troop buildup near Aleppo

(CBS News) The fierce fighting is getting even worse in the streets of Aleppo. Syrian army tanks and helicopter gunships are pounding rebel held neighborhoods.

There were sustained, loud explosions in the area of Aleppo, near where a CBS News crew was holed up Sunday night.

Locals say it's fighting between the government and the Free Syrian Army over at a nearby airbase.

The second-in-command for the rebels in Aleppo says he is concerned that forces are arriving in large numbers around the city. They've seen an increase in both tanks and troops. The rebels believe that a large-scale assault is imminent. Yet they point out that fighting has continued in the past few days anyway.

The rebel officer said his men can fight the Syrian Army soldiers in the street, but when tanks are used, his men can keep out of the way, but it's the civilian population that suffers. The officer said that rebel fighters continue to hold ground but there are discrepancies among the brigades.

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One local commander told CBS News that they are so low on ammunition that they can only defend instead of attack, and even then his brigade only has enough firepower to hold on for four or five days.

The humanitarian crisis seems to be getting worse by the hour, and especially worse in the past 24 hours. Refugees arriving from Aleppo spoke of indiscriminate shelling, and the civilians are running out of food and water after being under siege for nearly 2 weeks.

Additionally, it's not just the civilians facing shortages. One rebel brigade became so desperate Saturday night, the fighters actually tried to raid the food storage building near a Syrian Army base near Aleppo, and of course they were engaged. On Sunday they held a funeral for one fighter who was shot dead while trying to steal some eggs.