A few minutes of searching, and I stumbled upon what looked like artillery guns at the stadium's main gate. I asked a renowned weapons expert to analyze the images. Wim Zwijnenburg of Dutch peace organization Pax identified them as Soviet origin D30 122 mm howitzers.
Here's a file photo of the model. They have a range of up to 15km, but with self propelled ammunition they can hit targets 20km away. This brings many rebel held villages within striking distance.