An overnight suicide blast in Beirut's southern suburbs, Hezbollah's main bastion, killed a security officer who had tried to stop the bomber, the General Security agency said Tuesday.
No one has claimed the attack, but an audio recording posted on YouTube by a Sunni militant group said there would be more "strikes" if the Shiite movement does not pull out of Syria.
The explosion happened around midnight (2100 GMT Monday) near an army checkpoint and cafe where football fans were watching a World Cup match.
An army statement said a suicide attacker driving a white Mercedes "blew himself up at an army checkpoint at the Tayuneh roundabout (in southern Beirut), wounding several civilians."
The official National News Agency reported 12 people wounded.
On Tuesday, the General Security agency confirmed in a statement that Abdel Karim Hodroj, a 20-year-old inspector, had been killed, after carrying out DNA tests on his remains.
"The martyr Hodroj paid with his life for the mission he was entrusted with, in the national war against terror," said the agency.
A security source had earlier told AFP that Hodroj and his colleague Ali Jaber, who was wounded, "were passing through the area ... They felt a vehicle that was going against the traffic flow was suspicious.
"The vehicle stopped in the middle of the road, and a man got out. (Hodroj and his colleague) stopped him and questioned him. The man said his car key was broken, and he couldn't drive any more," the source said.
The driver's suspicious behaviour led Jaber to go to the nearby army checkpoint to report him.
"Hodroj remained with the suicide attacker to ensure he wouldn't get away," the security source said.
Jaber was 30 metres (yards) away when the explosion happened.
- Terrorist plan -
The General Security statement added: "The martyr sacrificed himself to save a significant number of soldiers and civilians who would have fallen victim to the terrorist's plan."
The bombing came three days after a suicide attack in eastern Lebanon killed one person and wounded 30.
Southern Beirut, a stronghold of Lebanon's Shiite movement Hezbollah, has been targeted by attacks for months.
Most incidents were claimed by Sunni extremists because Hezbollah sent thousands of fighters into neighbouring Syria to support President Bashar al-Assad's forces battling rebels.
On Tuesday, a radical Sunni cleric warned Hezbollah in a voice recording distributed on YouTube of more possible strikes.
Sheikh Sirajeddine Zureiqat, who is linked to the Abdallah Azzam Brigades, did not claim responsibility for Monday's attack.
He said: "O party of Iran (Hezbollah), you who are an occupying force in Lebanon, you will not enjoy a single day of safety, until safety returns to the people of Syria and Lebanon."
"We will continue to strike you, as long as you continue to be present in Syria."
Zureiqat also called on Lebanon's Sunnis to take up arms "to defend the oppressed" and "avenge" the bloodshed in Syria.
The Abdallah Azzam brigades are an Al-Qaeda-linked group that has previously claimed responsibility for other Syria-related violence in Lebanon.