ALEPPO, SYRIA // Syrian rebels turned a captured tank against government forces today and bombarded a military airbase, a welcome boost to their firepower in the week-long battle for the country's commercial capital Aleppo.
Meanwhile, troops loyal to Bashar Al Assad, the Syrian president, pounded the strategic Salaheddine district in Aleppo itself with tank and artillery fire while rebels tried to consolidate their hold on areas they have seized.
In the capital Damascus, troops overran a suburb on yesterday and killed at least 35 people, mostly unarmed civilians, residents and activist organisations said.
The fighting for Syria's two biggest cities highlights the country's rapid slide into full-scale civil war 17 months on from the peaceful street protests that marked the start of the anti-Assad uprising.
World powers have watched with mounting concern as diplomatic efforts to find a negotiated solution have faltered and violence that has already claimed an estimated 18,000 lives worsens.
However, in a shift toward increased foreign involvement in the war, Barack Obama, the US president, has signed a secret order authorising American support for the rebels, according to US sources familiar with the matter.
The order, approved earlier this year, broadly permits the CIA and other US agencies to provide support that could help the rebels oust Mr Assad.
The lightly armed insurgents are battling a well-equipped army that has overwhelming superiority on paper. The rebels' moral was boosted when they turned a government tank's gun on the Menakh airbase 35 kilometres north of Aleppo, a possible staging post for reinforcements for the army's attack on Aleppo.
"We hit the airport using a tank that we captured from the Assad army. We attacked the airport a few times but we have decided to retreat at this time," a rebel fighter named Abu Ali said.
The pro-opposition Syrian Observatory for Human Rights said government forces at the airbase had used artillery and rocket launchers to bombard the town of Tel Rifaat, which lies between the airbase and Aleppo.
Reuters correspondents heard heavy weapons fire on Thursday morning from Salaheddine in south-west Aleppo, a gateway to the city of 2.5 million people that has been fought over for the past week.
Heavily armed government troops are trying to drive a force of a few thousand rebel fighters from the city in battle whose outcome could be a turning point in the conflict.
Although government forces have made concerted efforts to take Salaheddine, a full-out assault on the city as a whole has yet to take place.
In Damascus, still a government stronghold but a scene of combat in the past two weeks, government troops faced new accusations of atrocities after they overran a suburb on Wednesday.
"When the streets were clear we found the bodies of at least 35 men," a resident, who gave his name as Fares, said by phone from Jdeidet Artouz, south-west of Damascus.
"Almost all of them were executed with bullets to their face, head and neck in homes, gardens and basements."