Lebanon's militant Hezbollah group said Friday that its top military commander who was supervising its military operations in Syria, Mustafa Badreddine, was killed in an explosion in Damascus, a major blow to the Shiite group which has played a significant role in the conflict next door.br Badreddine, 55, had been the mastermind of the group's involvement in Syria's civil war since Hezbollah fighters joined the battle on the side of Syrian President Bashar Assad's forces against those trying to remove him from power, according to pro-Hezbollah media.br Hezbollah, along with Iran, has been one of Assad's strongest backers.br Hezbollah said several others were wounded in the blast and that it was investigating the nature of the explosion and whether it was the result of an air raid, missile attack or artillery shelling.