At least seven people, including two children, were killed and 30 others wounded Thursday by suspected rebel shelling targeting a number of districts in the country's northwestern province of Aleppo, the state news agency SANA reported. The bombardment struck the districts of Sulaimaniyeh, Midan and Maysalun in Aleppo and caused material damage, said the agency, adding that some of those wounded by the attack are in critical condition. The incident is the latest in a string of similar shelling attacks by suspected militant groups, which have used such tactics to shake the government's grip on the area and to retaliate against the Syrian army's advancement on many fronts in central and southern Syria. A day earlier, the Syrian Observatory for Human Rights, a London-based watchdog group that relies on a network of activists on ground in the country, said that Syrian government aircraft dropped explosive-laden barrels on rebel-held areas in Aleppo, but did not report any casualties. Meanwhile, the state news agency said the Syrian troops killed many suspected rebels in the southern province of Daraa, namely in towns of Sheikh Miskeen, Tsil, Naiymeh and Musaifra. Government troops also ambushed another insurgent group in the northwestern province of Idlib, according to SANA. The three-year crisis started in mid-March 2011 when anti- government protesters took to the street calling for reforms, but rapidly evolved into a civil war which witnessed the formation of anti-government militias joined by radical jihadist movements. Reports estimate more than 150,000 people have been killed so far.