A hunch by a young Lebanese security officer prevented a potential massacre as scores of people watched a World Cup match in Beirut, but it also cost his own life.

The intuition and bravery of 20-year-old General Security agency inspector Abdel Karim Hodroj meant he was hailed as a hero on Tuesday.

Hodroj had been driving home late on Monday with a colleague, Ali Jaber, when they saw a white Mercedes driving against the traffic flow towards the cafe, a senior General Security official said.

At the time the south Beirut cafe was packed with scores of people watching the Brazil-Cameroon clash.

"The vehicle stopped in the middle of the road, and a man got out. (Hodroj and Jaber) stopped him and questioned him. The man said his car key was broken, and he couldn't drive any more," the official said on condition of anonymity.

The two officers were immediately on guard in a country where car bombings are common, and south Beirut -- heartland of Lebanon's Hezbollah organisation -- has been a frequent target.

Jaber went to the closest army checkpoint to report his suspicions, while Hodroj stayed to ensure the man did not get away, the official said.

Jaber was 30 metres (yards) away when "the explosion happened", he added.

Hodroj was killed, and Jaber and several bystanders were wounded.

The densely populated Shiite neighbourhood of Shiyah was in shock Tuesday, as Hodroj's 47-year-old father Fadel received condolences at a hall in the Two Martyrs Cemetery.

"Your son is a hero," one visitor told the bereaved shopkeeper whose eyes were red with tears as he chain-smoked to help him cope with the pain and muttered "God keep you" to mourners.

"He saved the neighbourhood. He saved us from a massacre. We consider him a hero. We are proud of him," Hodroj's uncle said.

Hodroj was the sole fatality of the car bombing that the official National News Agency said also wounded 12 people.

"Some 200 people were watching the match. Abdel Karim (Hodroj) loved football and was impatient to watch his favourite team Italy play Uruguay on Tuesday," his uncle said.

"He was so young. We should have been organising his wedding, not his funeral ceremony."

The pain of loss was especially difficult to bear for Hodroj's father Fadel -- Abdel Karim was his only son.

A photograph at the funeral depicted a young man with black hair, fine features and smiling mischievous eyes.

He joined the General Security agency just 18 months before he died. An inspector, he worked in its IT department.

Elie, who studied with Hodroj, said: "Everyone liked him. He loved life, and was enthusiastic about his work."

His uncle added: "He loved to joke, and put everyone at ease. Anyone he'd meet would soon feel he was an old friend."

Hodroj's black-clad mother and her two sisters sat in another room, mourning their loss. The family is from the Shiite village of Bazuriyeh in southern Lebanon.

The explosion that killed Hodroj took place at midnight Beirut time (2100 GMT Monday), at the entrance to the Shiyah district.

An AFP photographer saw several cars ablaze as firemen fought to douse the flames and ambulances ferried the wounded to hospital.

The attack came just three days after a suicide bombing in the east of Lebanon killed one person and wounded around 30.

"The war against terror is being fought all across the world. In Lebanon, there are sleeper cells. When the conditions are there -- like in Iraq -- or when the political situation is especially unstable in Lebanon, the cells wake up," a high-ranking General Security official said.

The official also said the US intelligence services had warned Lebanon that new "terror" strikes were imminent.

"All the country's security services were mobilised to try to stop them," he said.

Southern Beirut, a stronghold of Lebanon's Shiite movement Hezbollah, has been targeted by attacks for months.

Most of the attacks were claimed by Sunni extremists who said they were because Hezbollah sent thousands of fighters into neighbouring Syria to support President Bashar al-Assad's forces battling rebels.