Syrian helicopters pound Aleppo, as massive onslaught looms

Tanks and armored carriers reportedly headed into Aleppo; Turkey calls for steps by international community.

TAL RIFAAT, Syria - Military helicopters pounded a fighters-held district of Aleppo on Saturday and armored units positioned themselves for an onslaught that could determine the fate of Syria's biggest city, opposition sources said.

Turkey, once a friend but now a fierce critic of the Syrian government, joined growing diplomatic pressure on President Bashar Assad, calling for international steps to deal with the military buildup.

The Syrian Observatory for Human Rights, an opposition group that collects information on the 16-month-old uprising against Assad, reported helicopter attacks on Aleppo's central Salaheddine district and fighting elsewhere in the city.

"Helicopters are participating in clashes at the entrance of Salaheddine district and bombarding it," the group said in an emailed statement. "There are also violent clashes at the entrances to Sakhour district."