BEIRUT — An impending battle for the northern city of Aleppo could prove to be a decisive moment for both sides in the Syrian conflict, threatening President Bashar Assad with a loss he may not survive or rebels with a rout that would highlight their disorganization and lack of firepower.
Government troops and rebel forces were massing Friday around Syria's commercial capital and richest city. Until a rebel offensive swept in from the outskirts this week, the city had been relatively calm and firmly under government control.
Syrian state television played martial music and showed stock footage of fervent conscripts signing up for military service. Assad was shown in camouflage, peering into binoculars alongside military commanders. Although the footage was probably shot long ago, playing it now emphasized the importance of the moment. In a front-page headline, the pro-government Al Watan newspaper spoke of a "Mother of All Battles" for the city of 2 million people.
The United Nations human rights chief voiced "deep alarm" over the build-up of forces in Aleppo, saying it "bodes ill for the people of that city."
U.S. officials warned of a possible massacre reminiscent of fears during last year's Libyan uprising for the rebel city of Benghazi. Western-led air strikes destroyed Moammar Gadhafi's mechanized columns, saving the city from being overrun.
But, mindful of the complexity of the Syrian conflict, Western officials have said consistently that they do not intend to intervene in Syria. That leaves government forces, heavily armed but stretched thin across the country, to battle poorly armed rebels who nevertheless appear to have seized the momentum.
Few doubt that the government will do everything it can to retain control of Aleppo, the country's economic hub, which is also the gateway to northern Syria.
"Assad can not afford to lose control of Aleppo," said Fawaz A. Gerges, director of the Middle East Centre at the London School of Economics. "It is as important as Damascus, if not more so, to Assad's survival."
A rebel-held Aleppo could morph into a kind of Syrian Benghazi, opening the way for the rebels to control northern Syria and create an opposition safe haven just 200 miles from Damascus, the capital. The region also is close to rebel supply lines in neighboring Turkey.
"Aleppo is so strategically located, next to Turkey, that it could serve as a beachhead to attack Assad's forces elsewhere," Gerges said via email. "In a word, the loss of Aleppo would effectively mean the beginning of the end of Assad's rule."
The fall of Aleppo would also be a devastating symbolic blow for a government that has already seen broad swaths of territory fall into rebel hands and has lost control of several border crossings.
On Friday, the people of Aleppo lived with profound apprehension as rumors swirled of an impending assault.
Unconfirmed opposition reports said there were as many as 80 tanks perched on the city's periphery, ready to strike. Many residents fled the city and others moved to districts judged safer, staying in mosques, schools or parks, said one opposition activist. Still, the opposition reported that people ventured out for traditional Friday protests calling for Assad's ouster.
The opposition reported another day of attacks by helicopter gunships and intense shelling, especially in the rebel-held southern district of Firdous. Video uploaded onto YouTube and said to be from the Firdous area depicts a cameraman in sandals striding through blood-stained streets and residents carrying bloodied and mangled bodies from the scene.
The Syrian military has been battered by defections and stretched thin as the rebellion has spread far and wide. Still, it enjoys a significant advantage in arms, including armored vehicles, tanks and aircraft, and remains a professional and well-trained force.
The fight for Aleppo poses a steep challenge for the Free Syrian Army and other rebel groups, who appeared to have seized the initiative since a bomb attack recently in Damascus killed key members of Assad's security team.
That strike appears to have opened a new phase, with the focus of the fighting shifting from the provinces to Damascus and Aleppo. Still, the rebels remain an assortment of militias lacking central leadership and a coherent political vision other than overthrowing Assad.
Money and arms have streamed into the rebel cause, much of it reportedly from gulf sheikdoms, notably Qatar and Saudi Arabia. But many rebel commanders still complain of a lack of weapons, especially anti-tank guns and anti-aircraft missiles.
In recent days, the government appears to have reasserted control in Damascus after heavy fighting. State television has shown graphic images of bloodied corpses described as dead "terrorists," as the government calls rebels, along with footage of troops firing intensely at insurgent positions.