At least 18 people were killed and more than 200 others wounded Thursday by a car bombing in a suburb of the Lebanese capital controlled by Lebanon's Shi'ite militant group Hezbollah.
Television footage showed chaotic scenes of walking wounded, shattered buildings and twisted, burning cars, while Beirut television reported gunfire near the blast scene. Firefighters used ladders to help residents escape their homes. There were no reports of arrests by late Thursday.
The attack is the second in the same area since Hezbollah fighters joined forces earlier this year with neighboring Syrian President Bashar al-Assad to battle Syria's Sunni-led rebels. A nearby bombing last month wounded more than 50 people.
A short while after Thursday's blast, an online video surfaced showing three masked men in front of a white flag inscribed with the Islamic profession of faith, Shahada. One of the three is heard describing the blast as a second message to Hezbollah chief Hassan Nasrallah.
Lebanese leaders on Thursday condemned the latest attack, and caretaker Prime Minister Najib Miqati declared Friday a day of national mourning.
The bombing follows Syrian opposition threats to target Hezbollah strongholds in southern Beirut and the Bekaa Valley towns of Hermel and Baalbek. Both towns, which are near Syria proper, have recently been hit by cross-border rocket fire.
The two-year Syrian civil war has devastated the country and killed more than 100,000 people.
Lebanese Army investigators inspect the site of a car bomb explosion in southern Beirut, August 16, 2013.
A forensic inspector examines a vehicle at the site of a car bomb in Beirut's southern suburbs, August 16, 2013.
Cars burn at the site of an explosion in Beirut's southern suburbs, August 15, 2013.
A woman cries at the site of an explosion in Beirut's southern suburbs, August 15, 2013.
People gather around the site of an explosion in Beirut's southern suburbs, August 15, 2013.
Smoke rises behind building from the site of an explosion in Beirut's southern suburbs, August 15, 2013.