BEIRUT: Lebanon's Hezbollah, blamed by Saad Hariri for his shock resignation as premier, has grown over the three decades since its founding into a mighty army used by Iran to project regional influence.
Hariri criticised the powerful Shiite movement for its meddling across the Middle East during a televised interview from Saudi Arabia on Sunday, his first media appearance since he stepped down on November 4.
Hezbollah has participated in Hariri's government for almost a year.
From Lebanon to Syria, Yemen, and Iraq, Hezbollah has matured into Iran's most useful "tool" -- drawing the ire of Tehran's regional rival Riyadh, analysts say.
Hariri's surprise resignation sparked worries that Lebanon would be caught in the crossfire of the bloody, decades-long power struggle between Saudi Arabia and Iran.
"This resignation indicates Saudi's will to put a stop to Iran's expansion," said international relations expert Karim Bitar.
Hezbollah had become Iran's "trump card" in the Middle East, added Bitar, of the Paris-based Institute of International and Strategic Affairs.
Since its founding in the 1980s during Lebanon's grinding war, Hezbollah has relied heavily on Iran for financial, political and military support.
It is the only faction to have retained its arsenal of weapons after the end of Lebanon's 15-year civil conflict in 1990.
Despite being branded a "terrorist" organisation by the United States and Gulf countries and targeted with economic sanctions, Hezbollah has risen to play a decisive role in regional conflicts.
- 'Most important tool' -
"The most important Iranian tool in the region is Hezbollah," said Hilal Khashan, political science professor at the American University of Beirut.
Hezbollah has trained Iraq's powerful Hashed al-Shaabi paramilitary forces, Khashan said, and even has "operatives" in Yemen's war to back Shiite Huthi rebels targeted by Riyadh.
Closer to home, Hezbollah has fought ferociously in Syria to defend the government of President Bashar al-Assad, also an ally of Iran.
The group's intervention in Syria's six-year conflict was a major turning point that helped Assad's troops retake swathes of territory.
It also helped hone Hezbollah's own combat experience, transforming it from a guerrilla movement to a powerful fighting force with offensive capabilities.
Combining its military expertise and political savvy, Hezbollah has matured into Iran's "crown jewel" in the Middle East, said Joseph Bahout at the Carnegie Foundation think tank.
It now serves as a "model" for all Iran-allied groups in the region, from Syria's pro-regime militias to Iraq's Hashed al-Shaabi and the Iran-backed Huthi fighters, Bahout said.
These military ventures formed the crux of Hariri's criticism of Hezbollah during his landmark interview on Sunday from Riyadh.
Breaking his silence more than a week after his resignation, Hariri called on Hezbollah to commit to Lebanon's policy to "disassociate" from regional conflicts.
"I tell Hezbollah: it is in your interest, if we want to protect Lebanon... to leave some of the areas that you have entered," Hariri said.
He zoned in on Yemen, saying Hezbollah's involvement in the protracted conflict there had drawn Saudi's rage: "Did the kingdom have any position towards Hezbollah before the war in Yemen?"
- Conflict 'flare up' -
Hariri, 47, accused Iran and Hezbollah of taking over his country and destabilising the broader region when he stepped down on November 4.
That announcement sparked worries that Lebanon would be sent careening back into political and economic turmoil as Riyadh and Tehran vie for influence.
There were even fears of a new war with Israel, after Hezbollah chief Hassan Nasrallah accused Saudi Arabia last week of asking Tel Aviv to bomb Lebanon.
Israel and Hezbollah have clashed several times, including in a month-long war in 2006 that killed 1,200 Lebanese -- mostly civilians -- and 160 Israelis, mostly soldiers.
But any new conflict between Lebanon and its southern neighbour risked spilling over into the broader region, experts have said.
"This time," said Bahout, "because of the extension in Syria and Iraq, it won't be a war on Hezbollah only. It will very quickly flare up."
Nasrallah's forces could respond to Israeli pressure by striking elsewhere, including the United Arab Emirates or even Saudi Arabia.
For Bitar, a convergence of factors, including "an impulsive Saudi Arabia, backed by an equally, extremely impulsive American president, and rising rhetoric in Israel", could indicate a war was near.
"But at this stage, we are still in a system where there is mutual deterrence, a balance of terror," he said.
"The two parties know that an eventual war would be devastating for both sides."