At least 13 people, including three children, have been killed after the Syrian army dropped a vacuum bomb on an elementary school in the northern city of Aleppo, according to Syrian opposition coalition officials.The opposition coalition announced on Wednesday that schools would be closed throughout the week amid the Syrian regime's intensified attacks on schools and residential areas."Thirteen people, including three children and three teachers, were killed when the Syrian regime bombed the Said al-Ansari school in the opposition-held Al-Ansari district," the National Coalition for Syrian Revolutionary and Opposition Forces said in a statement.No information was provided about the wounded.Many people were also killed after the Syrian army also dropped vacuum bombs in Aleppo's Bab al-Nairab, Balid, Saladin, Jab al-Qubba, al-Bayada, Sheikh Lutfi, Duwayr az Zaytun and Baskoy neighborhoods, according to opposition coalition officials' statement. Syria's civil conflict, which has entered its fifth year, has left tens of thousands of people dead and millions of others displaced both internally and externally.