Shells fired from war-torn Syria killed four people, including a child, when they rained down on the Lebanese border town of Arsal on Friday, a Lebanese security source said.
The deaths came as at least 20 rockets and shells launched from Syria hit border areas in the eastern Lebanon Bekaa Valley, which has seen frequent violence related to the Syrian conflict.
"At least four people, including a six-year-old, were killed and 20 others were injured when shells launched from across the border hit Arsal," said the security source.
"Other areas have also been shelled, including Ras Baalbek, Al-Qaa, Al-Ain and the edges of Hermel."
The town of Hermel is a stronghold of the Shiite Hezbollah movement in the Bekaa that was hit Thursday by a car bomb attack that killed three people.
The attack was later claimed by the jihadist Al-Nusra Front in Lebanon as a suicide operation.
Arsal is a Sunni area in the Bekaa that hosts thousands of Syrian refugees who have fled the violence in their country.
Its population sympathises strongly with the revolt in neighbouring Syria against President Bashar al-Assad.
Ahmad al-Hojairi, an official in Arsal, said it was unclear if Friday's casualties were Lebanese or Syrian.
"What we can confirm is that six or seven rockets launched from Syria hit a residential area. Two of the rockets hit houses."