BEIRUT -- Syrian government forces attacked rebels with helicopter gunships in the heart of Damascus yesterday, escalating a campaign to crush their opponents as clashes spread to new areas, illustrating the rebels' growing reach.

Cracks of gunfire and explosions echoed inside the capital for a third day, including a firefight near the parliament in an unprecedented challenge to government rule in President Bashar Assad's seat of power.

Iraq called on its citizens in Syria to return home, as the fighting overshadowed another round of diplomatic maneuvering, with special envoy Kofi Annan in Moscow pushing his faltering peace plan.

Plumes of gray smoke billowed over the Damascus skyline and helicopter gunships strafed the area, activists said,a sign the regime is growing desperate to push the rebels away from the capital.

Terrified families fled the city or said they were prepared to leave at a moment's notice.

"My bag has my family's passports, our university degrees, some cash and medicine," a 57-year-old father of two told The Associated Press, asking that his name not be used for fear of reprisals. "It is very hard to imagine leaving your home and everything you worked to get, but it's a matter of life and death."

Clashes were concentrated in the neighborhoods of Kfar Souseh, Nahr Aisha, Midan and Qadam, lower- and middle-to-upper-class districts in the city's southwest where street battles first erupted Sunday. Heavy clashes were also reported in Qaboun, a neighborhood in northeast Damascus.

Omar Qabouni, an activist in Qaboun, said eight people were killed yesterday in mortar and tank shelling by government forces. He estimated that about 300 rebels were taking part in the fighting.

UN Secretary General Ban Ki-moon arrived in Beijing in an effort to get Russia and China to back a tougher response to attacks by Assad's regime. Ban's trip comes ahead of a Security Council vote today on whether to allow sanctions and authorize actions to enforce them.

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