But UNIFIL officials said the casualties occurred when Lebanon responded to flights by Israeli warplanes over the area, in violation of a "blue line" the world body established more than three years ago, when Israeli troops withdrew from Lebanon, to demark the front-line areas.
An average of 20 such overflights has occurred in each of the past four months, UNIFIL said.
In response, Hezbollah artillery have been launching a barrage of anti-aircraft fire, UNIFIL said.
There had always been a risk that the artillery fire would fall into civilian areas of northern Israel, which appears to have been the cause of the Israeli casualties, UNIFIL added.
Gissin said Israel would seek to step up diplomatic pressure on Syria to rein in Hezbollah, which says it is only reacting to Israeli provocation.
Hezbollah has recently stepped up cross-border attacks in retaliation for what the militant Islamic group said was a targeted Israeli attack on one of its members.
Hezbollah said Friday it launched cross-border rocket and missile attacks against Israeli troops in the disputed Shaba'a Farms area where Israel, Lebanon and Syria intersect. Israel captured Shaba'a Farms during the 1967 Six-Day War.
After Friday's attack, Israeli Apache helicopters returned fire on Hezbollah positions in southern Lebanon.
Hezbollah, based in Lebanon, has stated its objective is to drive all "occupying" forces out of Lebanon. It waged a campaign for 18 years against Israeli occupation of southern Lebanon as a self-declared security zone. Israel withdrew its forces from Lebanon three years ago, but maintains a heavy military presence on Israel's northern frontier.