Description:U.N. troops respond to a large explosion in the southern Lebanese town of Tair Harfa, three miles from the border with Israel. There were no casualties in the blast. A Lebanese security source said it was caused by an unexploded rocket that had been fired into Lebanon during the 2006 war with Israel. But a spokesman for the U.N. peacekeeping force in Lebanon said soldiers in the area were still trying to determine the cause.(0:43)