Meanwhile, at the Nahr al-Bared refugee camp near Tripoli in north Lebanon, the military siege continued, with no quick end in sight.
The bomb in Beirut exploded on Monday evening in a Christian suburb, injuring 10 bystanders, a senior security official said.
Reports said the bomb exploded under an empty bus close to a commercial centre and a church in Bouchrieh, a residential and industrial area.
A series of bombings have occurred in and around Beirut since clashes between Fatah al-Islam fighters and Lebanese army forces began on May 20.
On Monday, the army resumed shelling the Nahr al-Bared refugee camp at around 9am local time (0600 GMT), targeting fighters from the Fatah al-Islam group holed up inside.
Fifteen days into the seige, Fatah al-Islam has refused to give up its weapons or surrender and is putting up stiff resistance.
Since Friday, the army has conducted an intensive assault on the group's positions at the camp's entrances with the aim of wiping out the group.
John Cookson, Al Jazeera's correspondent at Nahr al-Bared, said the Lebanese army called Monday's attack the "final stages" of its assault on the camp.
He said the attacks "came in waves", adding that "secret Lebanese security forces are inside the camp, electronically painting buildings they believe fighters are in. It takes hours, or even a day or so to get the guns lined up".
A 1969 agreement prevents the army from entering Lebanon's 12 Palestinian camps.
The violence, which erupted on May 20, is Lebanon's worst internal fighting since the 1975-1990 civil war.
At least 113 people have died and about 25,000 of Nahr al-Bared's 40,000 refugees have fled due to worsening humanitarian conditions.
"The Palestinian refugees are not being treated properly by Lebanon"
Sunny, Ottawa, Canada
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