At least 18 people were killed in central and northern Syria by either rebel-fired rockets or government aircraft bombing, the Syrian Observatory for Human Rights (SOHR) said on Tuesday.At least seven people, including six members of one family, were killed on Monday night in a military airstrike in the village of Um Hartein, east of the central province of Hama, Efe news agency reported citing SOHR.The NGO added that four other people were killed and several were injured in a similar attack in the town of Kourin, in the northern province of Idlib.In Aleppo, also in the north, at least three people were killed by rockets fired by insurgents in the area near government-controlled Shihan.Four others died in a military aircraft bombardment in the area of al-Owaina Kabira, in the southern outskirts of Aleppo.Syria has been engulfed in conflict for four years which has caused some 220,000 deaths, according to the UN.