But the Lebanese Shiite group blames the US for the rise of the self-styled Islamic State, and doesn't want to assist US efforts to unseat Syrian regime.
Lebanon's Army is seeking more US military equipment, including anti-tank missiles, after a tough fight earlier this month against Sunni jihadis that exposed its shortcomings.
The traditional enemy of Hezbollah has been Israel. But the Shiite group is now also defending the Syrian regime and Lebanon's borders from the Sunni Islamic State, stretching its resources.
The Lebanese militant organization is sending a small unit to assist Iran, its sponsor, in training Iraqi Shiite militia. Fighting in Syria and spillover onto Lebanese soil take priority for now.
Today's rockets launched from southern Lebanon were more likely a one-off, intended as a gesture of support for Palestinians, than a warning of a new campaign.
Hamas rockets have become more accurate and powerful, reaching well into Israel's economic and population centers. But Israel's Iron Dome defense system has so far been able to deflect them.
The Islamic State of Iraq and the Levant (ISIS) may be activating sleeper cells in Lebanon, which fears further spillover from wars in Iraq and Syria. Three bombers have struck over the last week.
Syrian regime gains in the strategic Qalamoun area face a counterattack by rebels holed up across the border in Lebanon. Post-Ottoman boundaries are dissolving in Syria, Lebanon, and Iraq.
Israel's top military officer warned today that Hezbollah's capabilities have grown substantially since the 2006 war, putting much of Israel within the reach of the Lebanese Shiite militant organization.
Lebanese parliamentarians failed to elect a successor to outgoing president Michel Suleiman. The power vacuum could end a reprieve from car bombings and rocket attacks.
The Syrian regime has clawed back substantial rebel-held territory in the last year – with critical help from Iran. Homs, the 'capital of the revolution,' is perhaps the most significant win.
Tfail, located on a spit of land that extends into Syria, is surrounded by Syrian forces on three sides. Hezbollah, a regime ally, sits on the fourth side.
Israel bombed Syrian military targets in retaliation for IED attacks on Israeli troops, allegedly by Hezbollah. By targeting Syria, Israel sent a message that it holds Damascus responsible.
The Syrian rebel stronghold of Yabroud fell to Hezbollah and regime forces this weekend, sending rebels fleeing to Lebanon. A spate of rocket attacks and bombings have followed.
A painstaking Hezbollah and regime offensive in Syria's Qalamoun region is coming to its climax. A victory would sever the main route to Lebanon for fleeing civilians and military supplies.
Hezbollah has incurred its greatest casualties ever while fighting for the Assad regime in Syria. Emotional funerals for fallen 'martyrs' are a way to keep up morale.
Israeli airstrikes: Israel has not commented on reports that it struck a Hezbollah target Monday night, but the circumstances and recent history point to its involvement.
Losing Qalamoun would be a blow, cutting off access to smuggling trails and the highway connecting Homs, Damascus, and the coast.
A steady stream of weapons from Iran and Russia, as well as those seized from Syrian Army storehouses, is being sold in Lebanon, reversing the flow of the war's early days.
A rebel victory in the strategic town of Qusayr would challenge the regime's narrative of a failing, divided opposition. The rebels' effort appears timed to gain clout in negotiations.
Rockets are flying in Lebanon's Bekaa Valley, adjacent to the Syrian border, with some apparently being fired from Syria, making the border feel increasingly irrelevant.
As a key backer of the Syrian regime, Iran may have leverage over President Assad that few parties can claim. But the UN has revoked its invitation to the Syria peace talks this week.
Former Lebanon Prime Minister Rafik Hariri was a pragmatist who had been holding secret weekly meetings with Hezbollah leader Hassan Nasrallah in the months leading up to his assassination.
The bombing follows Lebanon's arrest of a Saudi member of an Al Qaeda-linked group that bombed the Iranian embassy in Beirut in November.
Saudi Arabia is flexing its muscles in Lebanon, where the army is overshadowed by the powerful militant group Hezbollah, a key ally of Saudi rival Iran.