File Photo: Fighters from the Lebanese militant group Hezbollah, southern Lebanon, Sunday, May 21, 2023. AP
Wissam Dalla, a Syrian in his early twenties, "threw himself from the seventh floor" of a building where he had been staying with relatives "after learning his location had been discovered", Hezbollah said in a statement sent to AFP.
Dalla was "responsible for the explosion in the Sayyida Zeinab area" south of the Syrian capital last month, the Shia Muslim group added.
AFP was unable to independently confirm the allegations against Dalla.
Lebanese security forces played no role in the incident, a security source told AFP on condition of anonymity as they were not authorised to speak to the media.
Lebanon's authorities did not immediately issue any statements.
On July 27, six people were killed and at least 20 others wounded when a bomb exploded south of Damascus near the Sayyida Zeinab mausoleum, Syria's most visited Shia pilgrimage site, authorities said.
The Sunni Muslim extremist Islamic State group later claimed the blast, which came ahead of the annual commemoration of Ashura, a key event on the Shia calendar.
Friday's incident took place in Hay al-Sellom, an impoverished neighbourhood in Beirut's southern suburbs -- a Hezbollah stronghold.
The group had pursued Dalla amid fears he could carry out another attack, the statement added, saying he was taken to hospital but died.
"Relevant bodies" in Hezbollah were informed that he had entered Lebanon secretly, the statement said.
Hezbollah is the only Lebanese faction that kept its weapons after the end of the 1975-1990 civil war. It is considered a "terrorist" organisation by many Western governments.
Shia shrines are a frequent target of attacks by Sunni Muslim extremists, not only in Syria but also in neighbouring Iraq.
Syrian authorities had tightened security measures around the mausoleum for the 10-day Ashura commemoration.
Two days earlier, an explosion in a car in the same area wounded two civilians, official media had cited a security official as saying.
Hezbollah has been fighting on the side of President Bashar al-Assad in the country's civil war that erupted in 2011.
Beirut's southern suburbs saw a wave of bombings between 2013 and 2015 carried out by Sunni extremists in retaliation for the Shia group's intervention in the Syria conflict.