The Hezbollah militia, backed by Syria and Iran, is a powerful force set on inflicting as much damage as possible on Israel and able to call on thousands of rockets, missiles and fighters, experts say.
"They definitely do have very strong capabilities...More than anything, I would say they have resolve. They have quite strong determination," Krista Weigand, visiting scholar at the London School of Economics, said.
"They believe they are a legitimate resistance movement."
Founded in 1982 in response to Israel's invasion of Lebanon, the Shiite Muslim group kidnapped two Israeli soldiers on Wednesday, triggering waves of Israeli bombing that have so far left nearly 200 people dead and closed Beirut's airport.
In its unrelenting drive against Israel Hezbollah retains financial, military and ideological support from Syria and Iran, whose new firebrand President Mahmoud Ahmadinejad has called for Israel's destruction.
"There's no doubt that they (Iran) were instrumental in setting Hezbollah up," said Alex Bigham, a London-based Iran analyst at the Foreign Policy Centre.
"Evidence has been produced of military support, and there is also ideological support as well."
Weigand and Bigham said Iran contributed about 100 million dollars a year to Hezbollah, much of which is used for social programmes, but some is held for military purposes.
Quoting Israeli intelligence sources, the London specialist magazine Jane's Defence Weekly said Hezbollah probably had a total of 10,000 to 15,000 rockets provided by Syria and Iran.
The estimates square with claims made by the militia's leader, Hassan Nasrallah on May 23, when he said Hezbollah held 12,000 rockets.
Mustafa Alani, security director at the Dubai-based Gulf Research Centre (GRC), said Hezbollah possessed the Katyusha-122 rocket, which has a range of 29 kilometres (18 miles) and carries a 15 kilo (33 pound) warhead.
Hezbollah also possesses about 100 long-range missiles, some of which could hit Tel Aviv, the economic centre and site of many government buildings, experts said.
They include the Iranian-made Fajr-3 and Fajr-5, the latter with a range of 75 kilometres, enabling it to strike the Israeli port of Haifa, and the Zelsal-1 with an estimated 150-kilometre range, which includes Tel Aviv.
Fajr-3 missiles have a range of 40 kilometres, and a 45 kilo warhead, and Fajr-5 missiles, which extend to 72 kilometres, also hold 45 kilo warheads, Alani said.
According to Alani, the longer-range Fajr missiles would have a limited impact were they to hit a concrete buiding, barely penetrating the walls.
They would, however, cause damage similar to the attacks on the northern Israeli city of Haifa, where eight people were killed by a missile, were they to hit buildings with wooden roofs, Alani said.
These missiles "have more of a psychological impact, not a military impact," Alani said.
Israel's military strategy of bombing transportation routes to prevent Hezbollah from moving the two kidnapped Israeli soldiers, and also to limit its ability to move rockets, may soon have to give way to a ground offensive, Colin Shindler at the School of Oriental and African Studies (SOAS) said.
"The problem for Israel is that missiles are coming over the border and they seem to be reaching further into Israel on each day," said Shindler, a specialist in Israeli and Modern Jewish studies at SOAS in London.
"If that continues, Israel will go in and attempt to clear a broad swathe of territory above the Israel-Lebanon border."
Were Israel to invade Lebanon in an attempt to push Hezbollah back, they would likely encounter a militia made up of about 1,000 full-time Hezbollah members, along with a further 6,000-10,000 so-called volunteers, according to the GRC's Alani.
"If Israel invaded, we could see all those people involved, if not more," he said.
"This could drive a recruitment policy to get more volunteers."
By contrast, Israel's military is made up of more than 170,000 full-time soldiers, along with 408,000 reservists, according to The Military Balance, published by the International Institute of Strategic Studies in London.
In addition to that, it has more than 400 combat-ready aircraft, and along with its missile armoury, Israel also has nuclear capability with an estimated 200 warheads.
What then, are the chances of a peaceful resolution to a conflict bringing together Israel and a militia that was founded specifically to oppose it?
According to some analysts, none.
"Israel has expressed no interest in a rapid ceasefire, and even more importantly, the U.S. has made it quite clear that it would like this conflict to continue, to provide Israel with the opportunity to succeed," said Mouin Rabbani, a senior Middle East analyst at the International Crisis Group.
"There is no prospect of a mediated resolution."