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 can't hold ground against the government's heavy weapons.
Sunday, a group calling itself the "Brigade of Unification" announced in an online video that it was launching an operation in Aleppo, 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, fighting near President Bashar Assad's seat of power and a bomb blast that killed four top players in his regime's efforts to crush those seeking to end his rule. Rebels also captured several border crossings with Iraq and Turkey. The opposition's momentum put the regime on the defensive for the first time in the 16-month conflict.
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, the group said, including at least 24 government soldiers.
The escalating fighting is also feeding fears that Syria's war could spill across borders and spark a regional conflagration. 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.
The new rebel group announced its formation in another video this week that showed about 1,000 fighters, most wielding rifles, wearing camouflage and chanting "God is great!"