(CNN) -- A suicide car bomber killed four people and injured 27 others in a neighborhood in southern Beirut on Tuesday, Lebanon's state-run National News Agency reported.
Black plumes of smoke rose from Haret Hreik, which is known as a Hezbollah stronghold. Ambulances rushed to the scene, NNA reported.
The neighborhood is part of Hezbollah's high-security area known as "security square," and many of the Shiite Islamist group's leaders live there.
Troops have formed a security perimeter around the area and deployed investigators to the blast site, the Lebanese army said in a prepared statement.
The vehicle used in the attack was stolen, the army said.
A cryptic message claiming responsibility for the attack appeared on Twitter from a user with the name "al-Nusra Front in Lebanon." It claimed to be affiliated with the Syrian al Qaeda affiliate with the same name.
CNN cannot confirm the authenticity of the Twitter user or the claim. Al Nusra Front in Syria has not commented on the attack.
The message did not contain details that are typical of claims of responsibility by well-established terrorist groups.
In early January, four people died in Haret Hreik, and 77 more were injured, when a car bomb exploded, NNA reported.
The Islamic State of Iraq and Syria, a Sunni Islamist militant group, claimed responsibility for that attack, calling it the "first small payment" in a bigger push against the Lebanon-based Shiite militia Hezbollah.
ISIS, which is an affiliate of the al Qaeda terrorist organization, is one of the rebel groups fighting to overthrow autocratic Syrian President Bashar al-Assad.
Hezbollah -- also considered a terrorist organization by the United States -- is fighting beside al-Assad's troops, who are trying to quash the rebellion in Syria.