A small bomb exploded Wednesday on a main road near the eastern Lebanese city of Zahleh, killing at least one person and wounding 11 others, security officials and state media said.

It was not immediately clear what the bomb targeted. Lebanon has been hit by a wave of explosions over the past three years as Syria's civil war spilled over into its tiny neighbor, killing scores of people.

Security officials, speaking on condition of anonymity in line with regulations, said the bomb was placed on the side of a main highway linking eastern Lebanon with Beirut. Troops cordoned off the area and opened an investigation, they said.

The explosion came on a day when thousands of people were heading from the eastern Bekaa Valley to the southern port city of Tyre to participate in a rally marking the anniversary of the disappearance of a top Shiite cleric who went missing during a visit to Libya in 1978.

Imam Mousa al-Sadr, Lebanon's Shiite Muslim religious leader, flew to Tripoli for a week of talks with Libyan officials in August 1978. He was never seen or heard from again.

The state-run National News Agency quoted George Kitane, head of paramedics at the Lebanese Red Cross, as saying that the blast killed one person and wounded 11. He said two of the wounded were treated on the spot and the rest were taken to two hospitals in the area.

NNA said the bomb weighed less than 10 pounds and was placed by the side of the road.