Most of the casualties were soldiers, the officials said.
The officials said the car was booby-trapped and parked on a roadside. The bomb was detonated by remote control as the military bus drove by at the southern entrance to the northern city of Tripoli.
The explosion happened during morning rush hour, the officials said, speaking on condition of anonymity because they were not authorized to speak to the media.
Local TV showed soldiers sealing off the area and preventing people from approaching. The blast shattered windows in several cars parked in the area.
It was the second bomb attack in less than two months targeting troops in Tripoli, which has been rocked by sectarian fighting between pro-government Sunni fighters and pro-Syrian gunmen.
On Aug. 13,by a roadside bomb packed with nuts and bolts near a bus carrying troops in Tripoli. It was Lebanon's deadliest bombing in more than three years.
Meanwhile, CBS News' George Baghdadi reports that a hard-line Takfiri Islamic militant group was behind a deadlyon Saturday, according to a preliminary investigation. The blast left 17 people dead and another 14 wounded.
The car, rigged with about 400 pounds of explosive, exploded on a highway near a security installation on the road to the capital's airport road. The blast was also near the Sit Zeinab shrine, in a district which hosts at least half a million Iraqi and thousands of Iranian pilgrims.
Baghdadi reports no one had claimed responsibility for the bombing as of Monday morning.
It was the deadliest attack in the country since the 1980s.
"A preliminary investigation by specialized security bodies has revealed that the booby-trapped dark red suburban GMC entered the country on September 26, 2008 via a neighboring Arab state," said a report, run by official Syrian Arab News Agency.
Last week Syria reportedly deployed thousands of troops to its northern borders with Lebanon, as Syrian President Bashar al-Assad warned "extremist forces" were operating inside Lebanon to destabilize his country.