At least 33 persons were killed during air raids, believed to have been carried out by the US-led international coalition, against a school sheltering displaced people in the Syrian province of al-Raqqa, a media report said on Wednesday.The Syrian Observatory for Human Rights (SOHR) said that all the victims of the attack on Monday night were displaced people from other parts of the country, living in a school in al-Mansoura area, the Islamic State's main stronghold in Syria, Efe news reported.The 33 bodies were taken out from under the debris of the school that was apparently targeted in the air strikes.Residents from the area told SOHR that about 40 displaced families from the provinces of Homs and Aleppo were living in the school.SOHR did not rule out a rise in the deaths as there could be bodies still under the rubble.Since March 8, international coalition warplanes have intensified their attacks against the city of al-Raqqa and areas located east and west the homonymous province, where at least 116 civilians, including 18 minors, were killed during the bombings.