The rockets were fired from near the village of Seddiqine in the district of Tyre, the source said, without specifying who was responsible.
The Israeli army confirmed that four rockets were fired on Wednesday from southern Lebanon towards Israel, saying it retaliated with artillery fire.
"Four rockets were fired from Lebanon into Israeli territory" and Israel's air defences intercepted one while the rest "likely fell in open areas", it said in a statement.
"In response, IDF artillery are striking a number of targets in Lebanese territory," it said.
There were no immediate reports of any casualties.