The United Nations has held a ceremony to commemorate the deaths of 22 people in a suicide bombing of its main Baghdad office five years ago.
Flowers were laid at the UN's headquarters in New York on Tuesday to remember those killed in the attack, who included Sergio Vieira de Mello, the UN envoy to Iraq at the time.
"We grieve at their tragic deaths, yet we take heart from their courage," Ban Ki-Moon, the UN secretary general, told a gathering of UN staff, including some who were injured during the Baghdad attack.
A similar ceremony had been held earlier at the UN's office in Geneva, Switzerland.
The Baghdad blast remains the most deadly attack on the world organisation, which was set up in 1945.
Since 1948, when the UN established its first peacekeeping operation in the Middle East, 709 staff members have been killed around the world, including 42 last year.
Immediately following the bombing, in which 150 people were also injured, the UN dramatically scaled down its presence in Iraq.
The Baghdad bombing raised serious concerns over the UN's ability to protect its personnel serving in peacekeeping missions in hotspots around the world.
Some former diplomats have said the UN was too close to the US-led invasion forces in Iraq in 2003 and, in particular, to Paul Bremner, the head of the Coalition Provisional Authority at the time.
"The UN was a collaborator ... with Bremner, with the Americans and that would have been very visible to the Iraqis, particularly those who were Sunni or Shia or both, or others who were very unhappy, clearly, with the presence of Americans and the United Nations, " Denis Halliday, a former UN assistant secretary-general, told Al Jazeera.
Halliday said the UN should not have a presence in Iraq at all, while US troops are in the country.
"Only when the US is finally kicked out and if the government invites the UN should we go back in there and provide whatever assistance they determine we can best provide."
Last December, two suicide blasts targeting UN offices in Algeria killed 18 UN staffers, three of them foreign nationals.
Following the attacks, the UN staff union demanded an independent probe into whether adequate security measures were in place at UN facilities around the world.
In response, Ban assembled a six-member panel headed by former envoy Lakhdar Brahimi to investigate.
The bombings were claimed by an offshoot of Osama bin Laden's al-Qaeda group.