It is still unclear precisely which terrorist organization operating in South Lebanon fired at least five Katyusha rockets on Sunday, one of which landed inside Israel close to Kiryat Shmona.At the weekly cabinet meeting, Prime Minister Binyamin Netanyahu held the Lebanese government and Hezbollah responsible. So did Defense Minister Moshe Ya’alon, who warned “I do not recommend anyone test our tolerance and our determination to maintain the security of Israel’s citizens.Israel lodged a formal complaint with UNIFIL, the United Nations peacekeeping force stationed along the border with Lebanon, which has largely failed to live up to its mandate as stipulated in UN resolution 1701 and prevent Hezbollah from positioning missiles and rockets directed at Israel in apartments and residential areas in South Lebanon.But while the Lebanese government is ultimately the responsible party in this and other incidents of military aggression that spill over into Israel, the launching of Katyusha rockets might well have been carried out by a radical Sunni group.Bogged down in Syria helping President Basher Assad survive, Hezbollah presently has no interest in opening another front with Israel. Indeed, maintaining quiet on the southern border with Israel is a cardinal interest of the Hezbollah, at least for the time being.That’s why it makes more sense that the Katyusha rockets are a tactic being used by forces opposed to Hezbollah and to Assad. If the situation heats up on the border with Israel, reason these opponents, Hezbollah will be forced to spread its resources thinner and that means fewer Hezbollah soldiers on the ground in Syria fighting with Assad.Sectarian violence has deteriorated inside Lebanon in recent months, further exacerbated by a growing number of mostly Sunni Syrian refugees finding their way to Lebanon.The most recent chapter in the ongoing tragedy of sectarian civil war that has once again rocked Lebanon was the assassination on Friday of Mohamad Chatah. A former adviser to Sa’ad Hariri, Chatah was a leader of the March 14 Alliance created during the 2005 Cedar Revolution that mobilized hundreds of thousands of Christians, Druse, and moderate Sunnis and Shi’ites to protest against Syrian involvement in Lebanon. This coalition now supports the opposition forces fighting Assad. The assassination of Chatah was essentially a warning sent by the Hezbollah and the Syrian regime to their opponents, telling them to think twice before publicly challenging Hezbollah’s authority.Perhaps the Katyushas are the way of some radical Sunnis to send a message of their own to Hezbollah that the Shi’ite terror organization can be quickly and easily complicated in a confrontation with Israel. The Abdullah Azzam Brigades, a radical Sunni terrorist organization, took responsibility for previous rocket fire that hit northern Israel in August and for the assassination of senior Hezbollah member Hassan al-Laqqis earlier this month.Regardless of which terrorist organization is actually firing the rockets, however, Israel has a moral obligation to react quickly and with force to maintain deterrence.And that is precisely what the IDF did. On Monday Israel responded with dozens of mortar shells fired at Lebanon, signaling to the Lebanese government and to Hezbollah, a major political force in Lebanon with its own militia, that Israel will not tolerate any aggression. Ultimately, it will be the Lebanese government and Hezbollah that must be held responsible.The Katyusha attack was yet another reminder that while Israel is an island of relative stability in a region steeped with turmoil, we cannot remain immune to the spillover effects of the conflict rocking Lebanon.Our best strategy is to maintain a high level of deterrence.It must be made clear to the Lebanese government and to Hezbollah that they will pay a high price for allowing terrorist organizations of any kind to launch attacks against Israel.