Complex sentence: On 13 June, hundreds of Syrian army troops, backed by tanks, stormed Deir ez-Zor in response to attacks by Free Syrian Army in the past week which managed to destroyed several tanks and APCs and kill dozens of soldiers.
Split into simpler sentences: On 13 June, hundreds of Syrian army troops, backed by tanks, stormed the Deir ez-Zor city. Attack was response to attacks by Free Syrian Army in past week which managed to destroyed several tanks and APCs and kill dozens of soldiers.