Huge explosion in Hezbullahland

Lebanon's Daily Star is reporting on a massive explosion in Siddiqin, which is part of Hezbullah's southern Lebanon stronghold. If you look at the map above, find Kiryat Shmona on the right (the Israeli side has highway numbers which make it more legible) and then go directly left to the center, you will find Siddiqin. The Daily Star reports that - surprise - the explosion was probably caused by