Afghanistan is a potent symbol of the costs inherent in abandoning nations to the lawless forces of anarchy. That alone justifies international efforts to help rebuild the country. Lest there be any doubt, remember Sept. 11, 2001, and its worldwide reverberations. We learned then how a country, shorn of its civic institutions, becomes a vacuum to be filled by criminals and opportunists. In its chaos and poverty, Afghanistan became a home base for terrorism.

Must we learn that lesson all over again? The past six years have seen a massive international partnership to rebuild Afghanistan's state institutions. A modern constitution was adopted after widespread popular consultations. Presidential and parliamentary elections were held. Three million refugees returned from decades of exile. Clearly, a large majority of the population supports the international community's efforts on Afghans' behalf.

Yet, this progress is in jeopardy. Once again, the opportunists are on the rise, seeking anew to make Afghanistan a lawless place — a locus of instability, terrorism and drug trafficking. Their means are desperate: suicide bombs, kidnappings, the killing of government officials and hijacking of aid convoys. Almost more dismaying is the response of some outside Afghanistan, who react by calling for a disengagement or the full withdrawal of international forces. This would be a misjudgment of historic proportions, the repetition of a mistake that has already had terrible consequences.

The United Nations has been in Afghanistan for many decades. Our institutional memory stretches back to the traumas of the Taliban, and beyond to the era when rival militias battled one another for the meagre spoils of a country broken by civil war. Our hopes for the future look to a day when Afghan state institutions stand on their own, able to tackle with dignity the difficult tasks of reconstruction and development while providing security and justice within secure borders.

I believe that day is within reach. We cannot let it be lost to the inhuman violence of today's insurgents.

For all the frustrations and periodic setbacks, I am heartened by the strong and sustained international support given to Afghanistan. Security concerns notwithstanding, there has been obvious progress. Girls' school enrolment has increased dramatically in the past five years. Six million children are in schools today, compared to less than a million under the Taliban. More than five million children have been immunized against polio, crucial not only for them, but also for our fight to eradicate polio worldwide. Half a million Afghans have gained access to safe water.

New roads are helping farmers get produce to markets. Afghan farmers are meeting 95 per cent of the country's grain needs; in 2001, the figure was less than 50 per cent. The Afghanistan Independent Human Rights Commission, created following the 2001 Bonn Agreement, now has nine provincial offices, actively promoting human rights. Under the Taliban, women's participation in public and political life was non-existent. Today, 28 per cent of the seats in parliament are held by women.

The United Nations, alongside national and international counterparts, non-governmental organizations and Afghan civil society, will continue to provide the Afghan government whatever assistance it needs to build on these achievements. Our collective success depends on the continuing presence of the International Security Assistance Force, commanded by NATO and helping local governments in nearly every province to maintain security and carry out reconstruction projects.

In December, the Afghan National Army, supported by ISAF forces, reclaimed the town of Musa Qala in the southern province of Helmand, occupied by insurgents since February of 2007, and a major poppy-growing area. Significantly, it was led by the Afghan army and carried out at the request of the local population. At long last, development work can begin anew in Musa Qala.

The Afghan government has far to go before it regains control of its own destiny. But that day will come. It is hard work. There is little glory. It requires sacrifices. And that is why we are there.

Ban Ki-moon is Secretary-General of the United Nations.