The pitted roads around Multan, the city of saints, stretch flat across the fields. They lead past rundown factories, workshops, shabby roadside teashops and mile after mile of flat fields broken only by the mud and brick houses of the villages of Pakistan's rural poor. One road leads south-east to the nearby city of Bahawalpur, the biggest recruiting base of the militant groups currently being blamed by India for the Mumbai attack; another leads north-west to Faridkot, the home village of Mohammad Ajmal Mohammad Amin Kasab, a 21-year-old Pakistan national named yesterday in the Indian media as the only gunman involved in last week's atrocity now alive and in custody.

Already a picture claimed by the Indian media to be Kasab, showing a young man dressed in combat trousers, carrying a backpack and an AK47, on his way to to Mumbai's main station to carry out his deadly work, has become an iconic image of the assault on the city.

Two other militants have been named. Like Kasab, according to the Indian media reports, they are said to be from the Multan region, southern Punjab. They, too, are said to be members of the Pakistan-based militant group Lashkar-e-Taiba (Army of the Pure) and to have followed a five-month training period to prepare them for the attack. The charge of the group's involvement, denied by its spokesmen, has explosive political consequences for the volatile region and must be treated with caution. In the long-running contest between India and its neighbour, propaganda and misinformation is far from rare. But if the details now emerging are confirmed, the link to Pakistan may spark war.

For though it is widely acknowledged that Pakistan's civilian government has limited control over local militant groups, it is clear that Pakistan's military and security establishment does.

Lashkar-e-Taiba was originally founded with the support of the Pakistani military intelligence service, the ISI, to fight as 'deniable' proxies in the contested territory of Kashmir, part of a decades-old strategy by the militarily weaker Pakistan to 'bleed' its bigger rival. The ISI also has connections with Jaish-e-Mohammed, the second group that New Delhi security officials has accused of involvement in the Mumbai attacks.

For the moment little is known about the three men named yesterday or their accomplices. But their place of origin comes as no surprise to experts. Both Lashkar-e-Taiba and Jaish-e-Mohammed draw the majority of their recruits from the southern Punjab. Last week The Observer travelled to the twin towns of Multan and Bahawalpur, the centres of the region, to investigate the reality of the groups' power on the ground, their relations with the Pakistani intelligence services and the factors which drive young men, possibly including the Mumbai gunmen, to join them.

Trace a line from where US special forces battle Taliban fighters in the corner of empty desert where the Afghan, Pakistani and Iranian frontiers meet, follow it through the badlands of the Pakistani North West Frontier and on through the bomb-blasted cities of northern Pakistan and down through Delhi, attacked in September, to shell-shocked Mumbai, and one thing becomes clear: this zone has displaced the Middle East as the new central front in the struggle against Islamic militancy. The southern Punjab falls on the line's centre point. There may be doubt over the identity of the attackers, but there is none that Multan and Bahawalpur and villages such as Faridkot are in the Indians' sights.

For most militants in the region the story - and that of Azam Amir Kasab is unlikely to be very different - starts at school. The southern Punjab has one of the highest concentrations of religious schools or madrassas in south Asia. Most teach the ultra-conservative Deobandi strand of Islam that is also followed by the Afghan Taliban and, crucially in this desperately poor land, offers free classes, board and lodging to students.

In Bahawalpur the Jaish-e-Mohammed group, believed responsible for a string of brutal attacks across south Asia, including the murder of Jewish American journalist Daniel Pearl, has been linked to two such madrassas. One is the headquarters of the group - a semi-fortified and forbidding complex in the centre of the town. The other is the Dar-ul-Uloom Medina, where the brother-in-law of Rashid Rauf, the Bahawalpur-based suspected British militant thought to have been killed in an American missile attack eight days ago, is a teacher. Surrounded by some of the 700 students, he told The Observer that 'jihad' was the duty of all his young charges.

The pupils at the more radical Bahawalpur and Multan schools grow up soaked in extremist ideology. The most senior cleric in Bahawalpur, Maulana Riaz Chugti, said his students could only go 'for training or to fight' after their studies or when the schools were shut for the holy month of Ramadan.

'To fight in Afghanistan or Kashmir and to struggle against the forces who are against Islam is our religious duty,' Chugti, who oversees the education of 40,000 students, told The Observer.

In Bahawalpur both the effects and the limits of the recent reversal of policy by the ISI, the powerful Pakistani military intelligence service, are evident. A crackdown on the militant groups was launched after they were blamed for a bloody attack on the Indian parliament in 2001 which almost brought India and Pakistan to open war. The groups, previously seen as a strategic asset, were suddenly seen as, at least for the moment, a liability. When their operatives were linked to plots to assassinate the then President, and evidence of collusion with al-Qaeda itself became clear, the pressure mounted on the ISI to rein in their former protégés.

'The militants have had to lower their profile,' said one local security official. 'They are no longer recruiting or preaching or raising funds openly. Things are much more difficult for them. If they recruit at all they do it individual by individual, not en masse like before. There is no production line.'

But the groups - along with break-away outfits with their roots in sectarian Shia-Sunni violence in the region - still have a significant presence in the region, particularly in remote villages such as that of Azam Amir Kasab. 'They may be semi-retired, but in my village there are 300 men who have fought in Afghanistan and have training and can be activated with one phone call,' one local former militant said. That fighters for one operation should come from the same place was not surprising. 'When I went to Afghanistan I went with five guys who I knew from school,' he said.

The young men of the southern Punjab have been found across a broad swath of south Asia and even further afield. In Kabul in August, The Observer interviewed Abit, a 23-year-old from Bahawalpur who had surrendered to Afghan police seconds before he was supposed to blow himself up in a huge truck bomb. Other militants from the town have been found as far away as Bangladesh. Lashkar-e-Taiba members have even been located in Iraq.

The groups are also of great interest to British intelligence services, who fear their key role as intermediaries between young volunteers from the UK's Muslim community - such as Rauf - and al-Qaeda leaders based in the volatile tribal zones along Pakistan's western frontier. The groups, the sources say, have a UK support network to supply funding.

The groups' relationship with the intelligence services is complex. Front organisations for the groups have even put up candidates in recent elections and travel without fear throughout Pakistan. Earlier this year The Observer interviewed a representative of one group alleged to be linked to Lashkar-e-Taiba in the foyer of a luxury Lahore hotel.

Local politicians said groups in the region were still powerful enough to intimidate the local government and security forces and even to collect tax or mediate in legal disputes in some areas. Roshan Gilani, a Shia community leader in Bahawalpur, said music shops had received Taliban-style threats, telling them to close or risk violence. Prominent Shias have been told they are on a hit list.

Until the Mumbai attacks, the recent series of bombings in India had been attributed by most analysts to a home-grown militant outfit: the Indian Mujahideen. With many highly educated and middle-class recruits among its ranks, and led by a 36-year-old computer engineer, the group's members have a very different profile from the Pakistani groups' recruits. But though their paths may be very different, the militants' eventual destination - fanaticism, violence and hate - are the same.

Intelligence agencies have done much research since 9/11 into how individuals become terrorist killers. Dehumanising the enemy is seen as key. Civilians are no longer seen as innocent but as complicit in a war waged by their governments against Islam. Group dynamics also play a huge role, particularly when teams of militants are isolated from normal society for long periods of time. Training camps - such as those in which Azam Amir Kasab is said to have spent months - are the perfect way of reinforcing solidarity and the new 'world view' which will allow them to execute murderous operations, such as killing diners in a hotel restaurant in cold blood.

Indian authorities believe local members of the Indian Mujahideen may have acted as scouts to prepare the ground and gather intelligence before the attack. Security services now recognise that militant groups looking to prepare attacks seek out resources and often enter into temporary coalitions with other outfits when necessary. Though criminal links to Islamic militants are rare, they are not unknown, and there are some suggestions that local underworld networks may have been exploited to get the attackers to the targets by sea.

India's terror groups

Lashkar-e-Taiba (Army of the Pure)

Battling to end Indian rule in Kashmir, this Pakistan-based group is routinely blamed by Indian security forces for attacks. The surviving gunman arrested in Mumbai is said to be a member.

Maoists, also known as Naxalites

Prime Minister Manmohan Singh has said the Maoists are the most serious threat to national security. Their battles with police cause a steady death toll.

Liberation Tigers of Tamil Eelam

The violence caused by this Sri Lankabased separatist group spilled into India in 1991 when a suicide bomber killed Prime Minister Rajiv Gandhi.

Sikh separatists

President Indira Gandhi's Sikh bodyguards shot her in 1984 in revenge for the hundreds killed when the military, aiming to suppress separatist militants, stormed a temple in Amritsar. Riots followed.

Students Islamic Movement of India

An Islamist fundamentalist organisation. Indian police suspect involvement in the attack on Jaipur this summer.

United Liberation Front of Asom

Formed in 1979 to establish a 'socialist Assam' through armed struggle. One of many such groups in north-east India.