Security officials said four missiles hit a remote area on the edge of the Lebanese border town of Arsal. There were no reports of casualties.
The Syrian forces were believed to be chasing rebels in the area, which has been the site of clashes in the past between opposition fighters battling Syrian troops just on the other side of the frontier.
Lebanese armed forces have previously detained people in the region caught trying to smuggle weapons into Syria.
Arsal is a predominantly Sunni Muslim town, like the majority of Syria’s opposition that is trying to oust president Bashar al-Assad from power. Mr Assad belongs to the minority Alawite sect, an offshoot of Shiite Islam.
Syrian shells have hit Lebanese territory in the past, but the latest air raid appears to be the most serious violation. Several Lebanese, including a journalist, have previously been killed and dozens wounded by fire from the Syrian side.
Meanwhile, in Syria, troops shelled rebel-held areas including the city of Aleppo and the Damascus neighbourhood of Hajar Aswad, activists said. The UK-based Syrian Observatory for Human Rights and the Local Co-ordination Committees reported clashes between troops and rebels.
Source: Scotsman News