Syrian military helicopters pounded a central district of Aleppo on Saturday as forces loyal to President Bashar Assad prepared for an onslaught on rebel fighters that could determine the fate of the country's biggest city, opposition sources said.
Turkey, once a friend but now a fierce critic of the Syrian government, joined growing diplomatic pressure on Assad, calling for international steps to deal with the military build-up.
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The Syrian Observatory for Human Rights, an opposition group which collects information on the uprising against Assad that has gripped Syria for over 16 months, reported helicopter attacks on the central Salaheddine district of Aleppo and violent clashes 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."
The battle for the city of 2.5 million people is seen as a crucial test for a government that has committed major military resources to retaining control of its two main power centers, Aleppo and Damascus, in the face of a growing insurgency.
Early on Saturday morning, activists said Syrian tanks began moving in on south-western districts of the city, the BBC reported.
Rebels in Aleppo this week (Photo: AFP)
Three rebel fighters were killed in clashes between midnight and dawn on Saturday in Aleppo, the Observatory said. It said 160 people were reported killed in Syria on Friday, adding to an overall death toll of around 18,000 since the uprising began.
Video footage provided by the Observatory showed smoke rising over apartment blocks in the city into a hazy sky on Saturday. The sound of sporadic gunfire could be clearly heard.
Turkey calls for action
Turkish Prime Minister Tayyip Erdogan said late on Friday that international institutions needed to work together to address the military assault on Aleppo and Assad's threat to use chemical weapons against external enemies.
"There is a build-up in Aleppo, and the recent statements with respect to the use of weapons of mass destruction are actions that we cannot remain an observer or spectator to," he said at a joint news conference in London with British Prime Minister David Cameron.
"Steps need to be taken jointly within the United Nations Security Council, the Organization of Islamic Countries, the Arab League, and we must work together to try to overcome the situation," he said.
Earlier, Erdogan had cheered on the rebels.
"In Aleppo itself the regime is preparing for an attack with its tanks and helicopters ... My hope is that they'll get the necessary answer from the real sons of Syria," Erdogan said in remarks broadcast on Turkish TV channels.
Cameron said Britain and Turkey were concerned that Assad's government was about to carry out some "some truly appalling acts around and in the city of Aleppo".
UN rights chief Navi Pillay urged both Syrian government forces and rebels on Friday to spare civilians in Aleppo, voicing deep concern at the "likelihood of an imminent major confrontation" in the city reminiscent of other deadly assaults.
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