Last week, the Taliban slaughtered three aid workers and their driver in Logar province in Afghanistan, just south of Kabul. The fact that the aid workers were there trying to help disabled Afghan children was, from the Taliban's perspective, irrelevant. In a statement issued soon after the attack, the Taliban said, "We don't value their aid projects, and we don't think they are working for the progress of the country."

This was no isolated event. Around the world, humanitarian workers are being targeted as never before. This, in turn, is forcing aid agencies to re-evaluate how they deliver assistance and, in some instances, pull back, with devastating consequences for millions of people who rely on humanitarian aid to survive.

The effect of the latest attack is already being felt in Afghanistan. When I worked there in 2004 and 2005, Logar province was considered relatively safe. Now, it's becoming a no-go zone. Aid agencies have restricted staff movements in the area where the four workers were killed, and some are considering suspending operations in the province entirely.

Providing assistance in places such as Afghanistan always has been dangerous, yet this risk was traditionally mitigated by the fact that aid workers were rarely direct targets. Humanitarian staff worked closely with communities, building the acceptance and trust necessary to ensure their protection. Aid agencies based their security on the assumption that as long as they remained neutral, no one would see them as a threat.

In many conflicts, this assumption no longer holds true. Since January, 23 aid workers have been killed in Afghanistan, 20 in Somalia and 10 in Darfur. Over the past three years, aid workers also have been killed in the Central African Republic, Iraq, Lebanon, South Sudan and Sri Lanka.

Overall, attacks against aid workers almost doubled between 1997 and 2005. The vast majority of the victims were national staff working in their own countries.

Part of the reason for the increase has to do with the fragmented nature of many conflicts since the end of the Cold War. In places such as Afghanistan, the Darfur region of Sudan and Somalia, there are a bewildering array of warlords and armed groups, and community acceptance isn't much of a security guarantee if bandits control the surrounding roads.

There also has been a rise in politically motivated attacks. Many rebel and insurgent groups no longer see humanitarian workers as neutral or independent. Aid agencies have long criticized Western troops in Afghanistan and Iraq for carrying out small development projects, "blurring the lines" between military and humanitarian actors.

The problem is much deeper and more widespread, however. Many Western aid agencies have agendas, such as support for women's rights, that put them directly at odds with religiously motivated insurgents like the Taliban — who, for instance, go to great lengths to attack girls' schools.

There's also no denying the effect of Iraq. Attacks against humanitarian workers there shattered whatever remained of the taboo against such acts and did so in a way that captured massive media attention.

As humanitarian agencies continue re-evaluating how they provide assistance in dangerous conflicts, Iraq offers a possible glimpse of the future. The lack of security forced most aid agencies there to leave. Instead, they now try to provide services through remote programming, putting projects into effect through local partners. This method tends to be less efficient, however, and it also increases the potential for corruption.

The organizations that stayed have adopted precautions: Some dramatically limit the extent to which staff can travel, or even leave their compounds, which makes it difficult to deliver aid effectively. Other agencies have partnered with the military for protection, an approach that has been criticized within the humanitarian community for further eroding the line between the aid agencies and the military.

The stakes are high. In many conflicts, humanitarian assistance can be the difference between life and death. In Afghanistan, for instance, 45 percent of the population struggles to find enough to eat, while one in five children die before the age of 5. Increasingly, aid workers face an agonizing choice between their own safety and their sense of commitment to those most in need.

Michael Kleinman, a Truman National Security Fellow, has worked for humanitarian agencies in Afghanistan, Africa and Iraq. He wrote this commentary for the Los Angeles Times.