The United Nations staff union said Tuesday that 35 UN personnel were killed in action last year, including 25 civilians, DPA reported.
The 2011 deaths surpassed the number of 15 killed in 2010, but was lower than the 38 UN personnel killed in direct attacks against the UN in 2009.
The staff union said the UN suffered heavy personnel losses in three major attacks in 2011 in Afghanistan and Nigeria.
In April, an Afghan protest against the burning of the Koran in Florida turned violent, with a crowd storming the UN compound in Mazar-e-Sharif, killing three staff from Sweden, Romania and Norway, and four security guards from Nepal.
A car bomb struck the UN House in the Nigerian capital of Abuja on August 26, killing 11 staff members who worked for UN humanitarian and development agencies, including the UN Office for Drugs and Crime, the World Health Organization and the UN Children's Fund.
The third attack directed at the UN took place in October in Kandahar, Afghanistan, where the UN High Commissioner for Refugees maintained an office. Three Afghan staffers were killed.
"The UN staff members have become primary targets of attacks and unfortunately the organization is not doing enough to protect its personnel," said Barbara, president of the UN Staff Union in New York.