The Islamic State (IS) terror group has executed 33 people in Syria, a UK-based monitoring group said on Thursday.The Syrian Observatory for Human Rights (SOHR) said the IS carried out the mass killing in the the al-Mayadin desert near the city of Deir Ezzor on Wednesday morning, CNN reported.The monitoring group called it "the largest execution operation carried out by the IS in 2017".The report said the people were between ages 18 and 25 and were "killed by sharp tools". It added that it is unknown whether the victims were Syrian government forces, allied militia or rebel factions.