By Zaffar Abbas
BBC Islamabad correspondent
Some had hoped that Pakistan's crackdown on Islamic extremists would herald a period of religious harmony.
Officials had dared to believe that the relative peace of cities like Karachi and Quetta - targets of bomb attacks in recent months - was a sign of the campaign's success in eradicating religious extremism.
Sectarian violence has its roots in the earliest days of Islam
But two bloody attacks in the first week of October have proved them wrong.
The deadly incidents in Sialkot and Multan indicate that sectarian violence has come full circle.
Extremist groups are once again returning to the Punjab region where they began more than two decades ago.
The attacks also reveal that Sunni extremist groups have not been the only ones to
survive a recent ban.
New groups of Shia extremists sprung into life just as soon as the old ones were stifled by the authorities.
Differences between the majority Sunni and minority Shia Muslims date back to the very earliest days of Islam.
They are directly linked to the issue of succession following the death of Prophet Muhammad.
The Shia believe that after Prophet Muhammad's death, his son-in-law, Ali, should have been given the reins of administration.
They still regard him as the first imam or spiritual leader.
The Sunni, however, believe that the appointment of one of the Prophet's companions, Abu Bakr, as the first Caliph was correct.
The Sunnis also respect Ali as the fourth Caliph of Islam.
In AD661, Ali was murdered and his chief opponent, Muawiya, became Caliph. It was the death of Ali that led to the great schism between Sunnis and Shias.
Muawiya laid the foundation of family rule in Islam and he was later succeeded by his son, Yazid.
But Ali's son Hussein refused to accept his legitimacy, and fighting followed.
It is not yet clear who carried out the Multan attack
Hussein and his followers were massacred in battle near Karbala in AD680.
The deaths of both Ali and Hussein gave rise to the Shia characteristics of martyrdom and a sense of betrayal.
Even today, Shia all over the world commemorate the killing of Hussein with vast processions of mourning in Pakistan and other parts of the Muslim world.
Shia Islam has always been the rigid faith of the poor and oppressed, of those waiting for deliverance.
It is seen as a messianic faith - awaiting the coming of the "hidden imam", Allah's messenger, who will reverse their fortunes and herald the reign of divine justice.
Today, the Shia make up about 15% of the total worldwide Muslim population.
In Pakistan, as in most Islamic countries, the differences between Sunni and Shia were initially confined to academic debate, and violent incidents were extremely rare.
However, the situation took a dramatic turn in the early 1980s.
The change in the regional environment, and the emergence of a political, albeit violent, Islam, introduced a new phenomenon of sectarianism to Pakistan.
The Soviet invasion of Afghanistan brought funding from the US and Saudi Arabia for (mostly Sunni) Islamic radical groups to fight against Kabul.
The Islamic revolution that ended the monarchy in Shia Iran ushered in a new wave of Shia radicalism in the region.
And when the then Pakistani military ruler, General Zia-ul-Haq tried to introduce his own concept of Sunni Islam to the country, a bloody conflict broke out.
Radical groups like Sipah-e-Sahaba and Tehrik-e-Jafria have their roots in the policies of those days.
Many believe that during this period, Pakistan became the battle ground for a proxy war, a stage on which different countries and organisations belonging to various schools of extremist Islam supported members of their faith and belief.
The phenomenon of the Taleban also fuelled this violence, as a number of Sunni extremist groups found both a refuge and a training ground in Afghanistan.
The violence continued in different forms even after these countries stepped back.
In the last few years, new, more radical groups have emerged, and they target each other with venom.
Between the era of General Zia and General Musharraf, successive political governments tried to tackle the problem, but without much success.
The events of 11 September 2001 changed the world - Pakistan dumped the Taleban and, in 2002, President Musharraf launched a major campaign against Islamic extremists, banning several groups.
But within weeks many had resurfaced, with new names but the same old intentions.
They were again outlawed last year.
Yet recent history seems to suggest that declaring radical groups illegal does nothing to solve the problem.
In fact, some Sunni extremist groups have been refining their agenda, joining hands with suspected Al-Qa'eda groups in a so-called global jihad.
At least two groups have been found to be involved in attacks against other minorities, particularly Christians.
And yet another group was found to be involved in the two attacks on President Musharraf's life in December 2003.
The group's leader, Amjad Farooqui, was recently killed in a gun-battle with security forces.
Senior officials believe the present cycle of violence is partly sectarian, and partly linked to the campaign by the extremist groups to destabilise the government.
They say that, having been hit in Karachi and Quetta, the groups have now returned to the Punjab to carry out their activities.
Officials say the attack on the Sunni gathering in Multan also suggests that after a series of attacks against Shia mosques, a new group of extremists from within the community may have emerged to avenge the killings.
After a brief lull last year, 2004 has particularly been a bad year. Since 1980, more than 4,000 people have been killed in Shia-Sunni violence.
And with new and more ferocious groups emerging with an ever wider and more violent agenda, it is nearly impossible to say what form it may take in the coming months and years.