``UN staff have become moving targets,'' deputy secretary general Louise Frechette told the General Assembly. ``Member states are willing to send unarmed civilians into places where they will not send well-armed troops," Frechette said.

Stephen Lewis, deputy director of the children's fund UNICEF, said that agencies such as his would have to review their work methods and consider the possible use of armed guards and escorts.

This has been a dark week for the UN.

Two UN civilian staff were murdered in Burundi, a third was shot dead in Kosovo, and seven members of a UN military observation mission were kidnapped in a secessionist province of Georgia by gunmen demanding a 200,000-dollar ransom (four were later released).

The murders brought to 13 the number of civilians who have died on duty with theUN this year.

Last year 27 civilians were killed. This was the highest number on record and for the first time it exceeded the number of fatalities among UN peacekeeping troops.

Lewis told AFP in an interview that aid workers were at most risk in Africa, largely because most humanitarian aid missions were there. "But aid workers are also in danger in Kosovo, in Chechnya, and any country engaged in civil conflict where rebel groups and government armies don't feel constrained by humanitarian principles," he said.

At the same time, he said, a radical change in the nature of conflict was discernible in Africa. "It has its roots in the international community's failure to disarm" the guerrillas in Rwanda before the 1994 genocide, he said.

"You did not need to be an expert on Africa or an expert on conflict to know that if the camps were not disarmed there would be hell to pay," he said, adding, "We are paying that price today." If governments cannot protect aid workers, he said, "the SecurityCouncil must make provisions for security."

Frechette urged governments to investigate and prosecute killers "to the full extent of the law". She said only one person had ever been convicted and imprisoned for killing a UN staff member.

They should also provide funds to improve staff security. "Improved security is not a luxury," Frechette said, adding, "It should be viewed, as it would be in any private firm, as an essential operating cost."