By Louis Charbonneau and Michelle Nichols UNITED NATIONS (Reuters) - Chemical weapons were likely used in five out of seven attacks investigated by U.N. experts in Syria, where a 2 1/2-year civil war has killed more than 100,000 people, according to the final report of a U.N. inquiry published on Thursday. U.N. investigators said the deadly nerve agent sarin was likely used in four incidents, in one case on a large scale. "The United Nations Mission concludes that chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic," the final report by chief U.N. investigator Ake Sellstrom said. Syria's U.N. Ambassador Bashar Ja'afari and the opposition Syrian National Coalition did immediately comment on the 82-page report.