Syrian forces were believed to be chasing rebels across the border with Lebanon when they fired into the border town of Arsal.
Arsal is a predominantly Sunni Muslim town, like the majority of Syria's opposition that is trying to oust President Bashar Assad from power. Assad belongs to the minority Alawite sect, an offshoot of Shiite Islam.
Lebanese armed forces have in the past detained people in the region for trying to smuggle weapons into Syria from Lebanon.
More top news
EastEnders star Danny Dyer is set to marry his long-term girlfriend after she proposed to him ... and Katie Hopkins isn't happy.
Relations between the Royal family and the Chinese have not always been friendly - but William's visit is helping build bridges.
Vicky Worrall was stunned when she opened her Friday snack to find the huge crisp which is nearly 5 inches long and she is now selling it.