The dead of southern Lebanon watch the living from the sides of buildings and from lampposts, their faces staring out defiantly from posters, heads often superimposed on bodies of generic men in uniform. These are Hizbollah's martyrs: men killed fighting against Israel before it abandoned the occupation of the south in 2000 or in the numerous clashes since, including the bloody summer war of 2006.

The images are often the only public acknowledgement of the individuals who make up this most secretive of institutions: Hizbollah's military wing.

But an Observer investigation has discovered that this covert organisation is quietly but steadily replacing its dead and redoubling its recruitment efforts in anticipation of a new, and even more brutal, conflict. Hizbollah has embarked on a major expansion of its fighting capability and is now sending hundreds, if not thousands, of young men into intensive training camps in Lebanon, Syria and Iran to ready itself for war with Israel. 'It's not a matter of if,' says one fighter. 'It's a matter of when Sayed Hasan Nasrallah [Hizbollah chief] commands us.'

The group's policy of refusing to discuss military matters extends to the highest levels. In speeches and rare interviews, Nasrallah refuses to answer even the simplest questions about the military wing, never referring even to the fact that his eldest son, Hadi, was a fighter himself. Life as a Hizbollah fighter is anonymous until death. But meetings with fighters, activists, Lebanese security officials, the UN peacekeepers along the border and residents of south Lebanon and the southern suburbs of Beirut, where the group is most active, offered a glimpse inside the workings of a group rarely open to outsiders. None of the sources within the group can be named - Hizbollah has barred members from speaking with the Western media since the mysterious death of a top commander, Imad Mughniyeh, in a Damascus car bomb.

'The most important thing is to never talk,' says one fighter, who agreed to speak about the group without revealing his name or specific duties inside 'the Islamic Resistance of Lebanon', as the military wing of Hizbollah is known. 'From the moment we begin our training, we are told two things: never disobey an order and never talk about the resistance. Hizbollah is not a job, it is not a family. It is a mix of religion, honour, dignity and discipline. It is my life.'

But what is becoming more obvious, even as Hizbollah tries to hide it, is that the group has embarked on an unprecedented build-up of men, equipment and bunker-building in preparation for the war that almost everyone - Lebanese and Israeli - considers inevitable. 'The villages in the south are empty of men,' said one international official. 'They are all gone, training in Bekaa, Syria and Iran.'

A trip by The Observer through villages in the Hizbollah heartland confirmed a conspicuous lack of fighting-age men. Visible were several new martyr posters, but unlike the traditional ones they portrayed anonymous, fresh-faced youngsters without military garb. According to locals, these are boys who have been killed accidentally in the latest wave of training in Iran. In the city of Tyre, too, posters showing young men killed in training exercises are cropping up. One is of Ahmad Hashem, killed while instructing recruits in the use of rocket-propelled grenades.

The initial training and selection of recruits is done in Lebanon, with Iran preferred for training on specialities - use of certain weapons, RPGs and anti-tank missiles - that require firing live rounds. 'But mostly the training in Iran is in theoretical things: philosophy, religion. The best training for fighting is done here in Lebanon,' said a fighter. 'We are so close to Israel here that our training becomes real.'

Israeli official statements suggest the increasingly aggressive recruiting results from the heavy casualties suffered by the group in 2006, a notion dismissed by sources within Hizbollah and even by the US military. While Israel contends that between 500 and 700 Hizbollah fighters were killed, the group itself said that about 80 fighters had died. Hizbollah sources admit that the losses were double that figure, while the US military study decided the death toll was 184.

'How could they be lying so much?' asked one resident of the south. 'People would not tolerate not having a funeral or posters of their son or husband. If it were 700 dead fighters, we would all know. We'd know more people killed, we'd be hearing the complaints from the families. Where can you hide 700 dead bodies in south Lebanon? It's too small.'

Losses aside, before 2006 most observers also widely overestimated the size of the military group. Some analysts put it as high as 5,000 men with more than 10,000 reservists, including its allied Amal - meaning Hope - militia supporting them.

'Ridiculous,' says the Hizbollah member. 'Before 2006 there were not more than 1,000 professional fighters, guys who manned bunkers and conducted operations full-time. The rest are trained and armed but lead ordinary lives unless called upon.'

This assessment is supported by regional intelligence services and Lebanese Shias, but now signs of the militia's dramatic expansion are alarming Hizbollah's domestic and international enemies.

The US military study described Hizbollah's military wing as 'completely decentralised'. Its commanders famously exercised this independence when they refused orders by the top command to abandon Bint Jebel in 2006 - then under massive Israeli ground assault. The town did not fall and Hizbollah rank-and-file today laud the refusal of orders as one of the biggest victories in the war. Recruiters closely watch youngsters for this kind of nerve and self-motivation, selecting the most talented boys for advanced training when they reach adulthood.

Hizbollah fighters describe a series of units - built around specialities such as rocket teams, heavy weapons experts, infantry, scouts and or part-time basis. 'Some units will be sent for training or operations for one, even two, years. Others continue to work or go to school. But even if you work your life is still Hizbollah. They call and that's it - you go. Maybe you tell your boss or professors you're going to Qatar or something for family reasons. But you never tell anyone what you're really doing.'

The decision to expand both the military wing and the supporting militias stems not from the losses during the 2006 war but from Hizbollah's success as a conventional military force in that conflict, says a Lebanese army commander who has worked with the group, his view being confirmed by the US military study. 'They were guerrillas during the occupation but shocked Israel in the war by standing and fighting from fixed positions. Even badly outnumbered, they held territory with minimal losses even under assault from tank units,' he says. 'Now they want to expand to make sure they can stop the next invasion before the tanks reach the flat plains of the Bekaa, where Israel's armoured units will have the advantage.'

Another crisis driving the build-up is Lebanon's political conflict, which pits Hizbollah and its allies against a coalition of Sunni, Druze and Christians supporting the Western-backed government. Street fights between Sunnis and Shias are becoming commonplace but Hizbollah cannot afford to take its men away from the bunkers in the south to fight on the streets of Beirut, say members of Amal and the Lebanese army.

'They know they can't send their best fighters, or the Israelis could attack. Israel will always be their main focus. But they have access to many that are good enough to fight with rocks, sticks and maybe some guns. They're training those guys to fight the Sunnis in Beirut,' says the army officer.

One Hizbollah fighter says he hopes that the situation doesn't deteriorate into them taking up arms against other Lebanese groups, but admits it is possible. 'God willing, I will never fight a Lebanese, but I will if ordered.'

Apr 30, 2008 21:00 | Updated May 1, 2008 19:17

By ETGAR LEFKOVITS, AP AND JPOST.COM STAFF

Sirens pierced the air in a mournful two-minute wail heard throughout Israel on Thursday, in tribute to the six million Jews murdered by the Nazis, as the country marked its annual Holocaust Remembrance Day.