A bombing in the southern suburbs of Beirut on Thursday killed at least four people, according to officials, aggravating the soaring tensions between Sunnis and Shiites that threaten to propel Lebanon into full-blown sectarian conflict.

The bombing in the Shiite neighborhood of Haret Hreik, which is controlled by Lebanon’s Hezbollah movement, followed the assassination of a prominent Sunni figure in a bombing in downtown Beirut on Friday, affirming an escalating pattern of retaliatory bombings in recent months.