BEIRUT — A new rebel group boasting some 1,000 fighters launched an operation Sunday to capture Syria’s largest city, Aleppo, while government troops using helicopter gunships and heavy artillery rolled back opposition gains in the capital, Damascus.
The spread of fighting into a second major metropolis displayed the rebels’ growing confidence — even though they still cannot hold ground against the government’s heavy weapons — pushing Syria’s civil war toward a new phase of destructive urban combat.
On Sunday, however, a group calling itself the “brigade of unification” announced in an online video that it began an operation in Aleppo, Syria’s most populated city and a key commercial hub that has remained relatively quiet throughout the uprising.
“We gave the orders to march on Aleppo with the aim of liberating it,” said Col. Abdul-Jabbar Mohammed Akidi, one of the group’s leaders.
The push into Aleppo follows weeks of high-level military defections, soaring death tolls, fierce fighting near President Bashar Assad’s seat of power and a bomb blast that killed top officials in his regime’s efforts to crush those seeking to end his rule. Rebels also captured several border crossings with neighboring Iraq and Turkey. The opposition’s momentum put the regime on the defensive for the first time in the 17-month conflict.
While the gradual swelling of their ranks and increasing organization have allowed them to push into major cities, the rebels remain largely unable to hold ground against Mr. Assad’s forces and helpless before his helicopters.
Early Monday morning, Arab nations called on Mr. Assad to swiftly give up power in order to end his country’s unrest.
“There is agreement on the need for the rapid resignation of President Bashar al-Assad,” Sheikh Hamad bin Khalifa Al-Thani told journalists following a ministerial meeting of the Arab League in Doha.
The Arab League also urged the rebel Free Syrian Army to form a transitional government of national unity.
“We call on the opposition and the Free Syrian Army to form a government of national unity,” Sheikh Hamad said as he delivered the results of the Arab League meeting.
He urged Mr. Assad to make the “courageous” decision in order to save his country where fierce fighting raged on Sunday between government troops and rebels. He added that only one Arab League nation had expressed reservations over the adopted position.
The week’s violence pushed the death toll for the uprising above 19,000, according to the Britain-based Syrian Observatory for Human Rights. The group said July is likely to be the conflict’s deadliest month so far, with more than 2,750 people killed in the first three weeks — nearly as many as in the previous month.
More than 100 people were killed Sunday, including at least 24 government troops, the observatory said.
The escalating fighting is also stoking fear that Syria’s war could spill across borders and spark a regional conflagration. Mr. Assad’s regime is a bridge between Iran and the Lebanese Shiite militant group Hezbollah. On the other side, the uprising is largely driven by Syria’s Sunni Muslim majority, which has more natural links with the region’s Sunni nations such as Saudi Arabia.
Syria’s uprising began in March 2011 when the government violently tried to quash protests calling for political reform. As dissent spread and the death toll rose, scores of rebel groups formed to fight government troops, and the conflict evolved into a civil war.
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