A correspondent for the British newspaper The Guardian said rebels who infiltrated Syria's largest city during the past week are in position about a mile from the loyalist troops. He said the rebels are under continuous bombardment.
The government has moved troops from the Turkish border to Aleppo, activists told the BBC.
Haj Morea, the leader of the rebel forces in Aleppo, told The Daily Telegraph that they need help from the outside. So far, he said, foreign leaders have condemned massacres in Syria but provided little help.
"We have heard many promises but until now we have not seen it with our eyes or touched it with our hands. We really don't have anything to prevent the tanks or bombing by fighter jets," he said. "We can only win over the citizens of Aleppo to our side and hope that strength of the people is enough."
On July 18, rebels killed four top officials in Damascus and soon after seized control of parts of the capital. They were quickly driven out of Damascus by a government counterattack.
So far, Assad appears able to beat back rebel advances. But Gen. Robert Mood, who is leaving the post of head of the U.N. monitoring mission in Syria, said he believes the regime will fall.
"In my opinion it is only a matter of time before a regime that is using such heavy military power and disproportional violence against the civilian population is going to fall," the Norwegian general said.