On Thursday, an explosion in Beirut struck near a facility used by Hezbollah, the Shia political party and armed group that in recent months has become increasingly and more publicly involved in the conflict in neighbouring Syria. At least 290 people were injured in the blast, which occurred between the Bir el-Abed and Roueiss neighbourhoods - an area regarded as the heart of Beirut's Hezbollah territory. And Hezbollah's leader Hassan Nasrallah blamed Thursday's bombing on Sunni armed groups he calls Takfiri.