Border Security Force (BSF) troops on Thursday averted a major tragedy by defusing two mortar shells found in a border hamlet in Kathua district of Jammu and Kashmir, officials said.A resident of Karol Biddu village along the International Border (IB) found the shells and immediately informed the police and BSF, they added.Troops of the border guarding force along with police reached the site and defused the shells safely, the officials added.