A senior military official told The Associated Press the car packed with explosives was parked on the side of a road and detonated by remote control as the bus drove through the Bahsas neighborhood on the southern entrance to the northern port city of Tripoli.
Twenty five people were injured in the blast, which tossed the car about a dozen yards during morning rush hour, according to security officials, who declined to be identified because they were not authorized to speak to the media.
The car's owner showed up later at the blast site, according to several television stations, and was picked up by intelligence agents for questioning.
Tripoli, Lebanon's second largest city, has a Sunni majority and the region is a known stronghold for Sunni militants. Sectarian fighting involving pro-government Sunni fighters and gunmen of a pro-Syrian Alawite sect - an offshoot of Shiite Islam - killed and wounded dozens this summer in Tripoli before a truce.
On Aug. 13, 18 soldiers and civilians were killed by a roadside bomb near a bus carrying troops on a busy Tripoli street. It was Lebanon's deadliest bombing in more than three years.
Monday's explosion came two days after a massive bombing in the capital of neighboring Syria killed 17 people and wounded 14. Syria said Monday the attack was carried out by a suicide bomber from a Muslim extremist group and that the vehicle came from a neighboring Arab country.
An unnamed Syrian official quoted by the official news agency in Damascus on Monday condemned the attack.
Syria's opponents here blame the government in Damascus for bombings in Lebanon over the last three years, accusations Syria denies.
Sheik Daie al-Islam al-Shahal, founder of the fundamentalist Salafi Sunni movement in northern Lebanon, blamed Monday's attack on "external forces" and rejected suggestions Sunni militants were behind it.
"The false allegations and haste do not help stability and cause tensions," said al-Shahal, Lebanon's most powerful Salafist leader.
