A large explosion struck southern Lebanon near the border with Israel on Monday, the Lebanese official news agency reported. Lebanon's National News Agency said it was not clear what had caused the early Monday blast near the border town of Tair Harfa. Andrea Tenenti, a spokesman for the U.N. peacekeeping force in the area, UNIFIL, said its team was able to reach the site of the explosion and is investigating. Tenenti did not know what caused the blast and said there were no reports of casualties, the Associated Press reported.