GENEVA: Kathleen Cravero was the next in line to die after she watched a "teenager" shoot two UN colleagues in the head, but a security guard overpowered their attacker in Burundi and she survived.

Recalling the tragedy 10 years later, the former UN Humanitarian Coordinator in Burundi told AFP: "It was certainly traumatising. You never forget seeing your colleagues murdered. You never stop asking yourself why you were third in line.

"But what is most traumatising for me today is that there is still complete impunity for the perpetrators." More than 700 humanitarian workers have been killed in the past decade, but "not one perpetrator has been brought to justice," Cravero said and the danger is increasing as aid workers face an increasingly hostile environment, according to UN data.

In 1998, 69 humanitarian workers were killed, kidnapped or seriously injured in violent attacks, while in 2008, the figure shot up more than three times to 260. Yesterday, a French employee of the International Committee of the Red Cross (ICRC) was kidnapped in the war-torn Sudanese region of Darfur.

A day later, The Kadhafi Foundation, run by Libyan leader Moamer Kadhafi's son, said two of its employees have also been kidnapped in Darfur.

Amid the sharp rise in attacks, the United Nations this year named August 19 "World Humanitarian Day" to honour aid workers who have lost their lives promoting the humanitarian cause.

The date is the anniversary of the truck bomb attack on the UN headquarters at the Canal Hotel in Baghdad in 2003, when 22 people, including top UN envoy Sergio Vieira de Mello, were killed.

Highlighting attacks on aid workers during the UNHCR's annual meeting, the UN High Commissioner for Refugees Antonio Guterres said the complexity of modern conflict -- involving armies, militias, insurgent groups and bandits, has made relief work more dangerous. Attacks against aid workers "undermine not only the operations in question but the very foundations of humanitarian action," he added.

While the United Nations conducts internal investigations into security incidents, it cannot discipline perpetrators.

In one of the worst incidents against humanitarian staff, six ICRC workers were murdered while they were sleeping in a hospital in Chechnya in 1996.

"What we usually do is we go to our contacts on the ground to understand what happened," said Dorothy Krimitsas, an ICRC spokeswoman, but she would not comment on issues surrounding prosecution.

In Cravero's case, the Burundi government blamed rebels after a two-week investigation. "But no one was ever caught and punished for the incident," said Cravero, urging for more to be done to bring attackers to justice.

"The UN General Assembly should hold a session each year to review violence against humanitarian staff. There needs to be a understanding that the humanitarian staffs and have no political agenda," she said.