(CNN) -- A Sunni Islamist militant group claimed responsibility Saturday for a car bomb attack in Lebanon's capital two days earlier which killed four people and injured dozens.
The group, the Islamic State of Iraq and al-Sham, known as ISIS, said Thursday's suicide blast in southern Beirut was the "first small payment" in a bigger push against the Lebanon-based Shiite militia Hezbollah.
The al Qaeda-affiliated group has been pushing for a fundamentalist Islamic state carved out of northern Syria, while Hezbollah fighters have been supporting Syrian President Bashar al-Assad's brutal push to crush a rebellion there.
The ISIS statement said it targeted "the Shiite Satan party" -- meaning Hezbollah -- in order "to crush its strongholds in the heart of its home in what is called the security zone in the southern suburbs of Beirut on Thursday in a first small payment from the heavy account that is awaiting those wicked criminals."
The residential Harek Hreik district, where the car bomb exploded Thursday, is known as a Hezbollah stronghold.
Car bombings in the same area of Beirut in July and August killed dozens and injured hundreds.
And in November, a suicide bomb attack outside the Iranian Embassy, close to the neighborhood where Thursday's attack occurred, killed two dozen people and injured about 150.
Long-standing tensions in Lebanon have been exacerbated by the civil war raging on its doorstep in Syria, where sectarian divisions reflect those in Lebanon.
The Lebanese army said Saturday that the alleged chief of another Sunni jihadist group, the Abdullah Azzam Brigades, had died in custody after his health deteriorated.
Majed Al-Majed, a Saudi national, was detained in the past few days by the Lebanese army. His group has claimed responsibility for bombings in Lebanon and elsewhere.
Beirut-based Middle East analyst Rami Khouri told CNN that the recent surge in violence in Lebanon was part of larger, regional turmoil.
"We are seeing the greatest proxy war of modern times playing itself out in Lebanon and Syria and Iraq, that have now become really one battlefield in which two great ideological camps are fighting to the death like gladiators," he said.
Political divisions and ideological tensions in Lebanon go back several decades, Khouri said, but they have been reinforced by the emergence of radical Islamist terrorist groups, linked to al Qaeda, following the U.S.-led invasion of Iraq.
Hezbollah, which is backed by Iran, was designated as a terrorist group by the United States in 1995.
CNN's Mohammed Jamjoom contributed to this report.