Samantha Power marks the fifth year anniversary of Sergio Vieiro de Mello's assassination with a New York Times op-ed on terrorists' new front against aid workers.

Just as we Americans tried to make sense of [9-11], United Nations officials, nongovernmental workers and world leaders grappled with applying the lessons of August 19. But five years later -- and less than a week after Taliban forces in Afghanistan killed three female educators and a driver with the International Rescue Committee -- the individuals who carry out vital humanitarian and development work for the United Nations and nongovernmental organizations have never been more at risk.

The Baghdad bombing made it clear that the United Nations and humanitarian groups had moved from the 1990s, when their flags no longer offered them protection, to a phase in which their affiliations made them outright targets of Al Qaeda and other violent extremists.

One of the most dangerous places in the world for humanitarian workers is Somalia. The head of the United Nations Development Program's Somalia office was shot dead coming out of Mosque last month. And just yesterday, local World Food Program confirmed that employee Abdulkadir Diad Mohamed was killed while riding in his car.

In her essay, Power recommends steps the international community can take to keep aid workers safe. This includes spending more money on security for humanitarian organizations and, where possible, getting greater commitments from the host country to provide security. In places like Somalia where this latter option is not possible (and where the international community is not willing to expend many resources) aid workers may have no choice but to pull out. It is an unfortunate decision to have to make. As Power says, we need to do more to protect the protectors.