The murder of Gayle Williams in Kabul on Monday follows a string of attacks on humanitarian aid workers in Afghanistan this year. The first seven months have seen more than 120 attacks and the murder of 30 aid workers. A further 92 aid workers have been kidnapped. In August the Taliban murdered three foreign women and their Afghan driver in an ambush just outside Kabul, which was the bloodiest single attack on an international organisation in Afghanistan in recent years. The four were working for the US-based International Rescue Committee, which I worked for when I lived in the country.

The Taliban justify their attacks by claiming that the aid organisations are attempting to proselytise for Christianity, which is illegal in Afghanistan. A relatively high proportion of those killed have been women, and it is quite likely that the targeting of women is a deliberate policy. When I was working in Jalalabad in 2004, the Taliban blew up a bus of women election workers as part of their campaign to try to prevent women voting in that year's presidential election. Girls' schools are also regularly burnt to the ground because the Taliban object to the education of women.

The Taliban view aid workers as soft targets. We are unarmed and we tend not to accept military escorts, as that would affect our humanitarian status. However, it is impossible to do the job without going into the field and, although security precautions are taken, we are probably the simplest high-profile victim.

Targeting aid workers is also a good way to achieve a wider political objective of halting the reconstruction of the country and undermining the authority of its central government. Afghanistan is hugely dependent on international assistance and - unlike Iraq - there is still considerable support for the international presence. That support has shrunk in recent years, as many Afghans believe that most of the aid is not getting through to its intended recipients. The more the insurgents can isolate the international community from ordinary people, the easier it is to portray our presence as a straightforward occupation of their country.

In fact, when they were in government, the Taliban relied heavily on the international humanitarian community to make up for their total neglect of social programmes. "God will provide" was Mullah Omar's standard answer when asked about his government's plans for healthcare and education. What he really meant was that he was leaving the task to international aid workers.

This has led to a more complex relationship between aid organisations and insurgents than is often supposed. Many agencies have been in Afghanistan for decades. Most were based across the border in Peshawar during the jihad against the Russians, and their aid helped to sustain the families of the mujahideen, some of whom went on to form the Taliban. There are a network of personal connections, mediated through tribal elders, by which aid organisations continue to communicate with the Taliban, often seeking their informal permission to operate in certain areas. Last year the Taliban released four Red Cross workers, which they said had been kidnapped by "mistake". A spokesperson said: "We have nothing against the Red Cross and we are going to release them soon."

The US government has also tried to integrate the delivery of humanitarian assistance into its counter-insurgency campaigns in both Iraq and Afghanistan, which many aid organisations complain has reduced the "humanitarian space" within which we can operate. For most aid workers, political neutrality remains the best form of self-defence and the best way to gain access to crisis zones.

• Conor Foley's book, The Thin Blue Line: How Humanitarianism Went to War, has just been published conorfoley30@hotmail.com