Syrian president Bashar Al Assad's jet fighters and helicopters continue to pound Free Syrian Army rebels in Damascus, Aleppo and other battleground cities, contributing to a death toll reportedly as high as 320 in one town in a single week. Attacks by jet fighters on rebels in Damascus yesterday reportedly killed 60 people.

But the rebels are fighting back, aiming heavy machine guns – and, if one report is to be believed, U.S.-supplied Stinger missiles – at Al Assad's aircraft. Yesterday rebels apparently downed a Russian-made helicopter over Damascus, as seen in the video above. If confirmed, the smashed copter could boost the rebels' tally of destroyed aircraft to at least six, including an L-39 jet forced to crash, a MiG-23 fighter-bomber apparently brought down over eastern Syria and another MiG blown up on the ground.

Heavy machine guns appear to be the rebels' best defense against Al Assad's aircraft, even when they miss. "We’re using these anti-aircraft guns to force their planes to fly higher so they can’t hit their targets so accurately," Malik Al Kurdi, deputy commander of the Free Syrian Army, told Al Jazeera on Aug. 17.

At the time Al Kurdi denied the rebels had received heat-seeking Stinger missiles from the U.S. – though he wished they had. "If we had those missiles, we’d use them straight away," Al Kurdi said.

But the same day, an unnamed "a source in the Syrian opposition" told Al Arabiya the Free Syrian Army had taken delivery of 14 Stingers. In the 1980s, the CIA famously passed Stingers to mujahedeen fighters battling the Soviet Union in Afghanistan. There the shoulder-fired missiles took a heavy toll on Soviet warplanes, hastening the Soviets' retreat. In Iraq and Libya and America's own Afghanistan war, the fear of Stinger-style missiles kept U.S. air planners awake at night.

In parallel with beefing up their air defenses, the Syrian rebels have been lobbying the U.N. and sympathetic governments to install a no-fly zone enforced by jet fighters, similar to that imposed over Libya early last year. Two weeks ago U.S. Secretary of State Hillary Clinton confirmed a no-fly zone was on the table. But resistance from Al Assad-backer Russia – not to mention logistical and basing concerns – could make the protective zone unfeasible.

In any event, the Syrian regime is losing more and more aircraft as the fighting nears its 18th bloody month. The destruction of six or more of Al Assad's planes and copters might not mean the end of the airborne onslaught – Damascus does, after all, possess hundreds of aircraft. But the erosion of the government's aerial advantage could help sustain the insurgency after repeated setbacks in bitter urban ground fighting.

With both sides deploying heavier weaponry, and using it to greater effect, the Syrian civil war shows every sign of escalating ... and no sign of a rapid resolution.

Update, Aug. 30: So it appears one of the shoot-down videos – one depicting an L-39 trainer being forced down by gunfire – is actually a fake. At the same time, a new and apparently authentic video has surfaced of a regime MiG-21 being destroyed. So our count of shot-down government warplanes remains the same.