At least 17 of their colleagues died in the blast, including UN special representative Sergio Vieira de Mello, and more than 100 were injured.
UN workers have protested they are not the enemy.
They say they are only in the country to help it get back on its feet after the anarchy that followed the fall of Saddam Hussein.
And many Iraqis seem to share their opinion.
Hassan al Bazzaz, a professor of politics at Baghdad University, said the UN must continue with its work in Iraq to save the nation from its dire predicament.
He told Aljazeera: “The people of Iraq will absolutely be the first to be negatively affected by the consequences of such an attack.”
But although it may not be the most obvious target for a resistance attack, other Iraqis point out there are genuine reasons why the UN is a target.
Some point to a vote in the Security Council last week when the UN gave its approval to the American-appointed Iraqi Governing Council.
This may have been like a red rag to a bull for Iraqi resistance groups who argue the council is illegitimate and does not represent the people.
The UN is blamed for punitive
sanctions against Iraq
The UN vote was seen by some as legitimising the American occupation of the country.
And many Iraqis remind foreigners the UN was the body which maintained punitive sanctions on Iraq for 14 years.
A 1999 Unicef report said more than half a million children had died as a direct result of sanctions.
Meanwhile, Saddam Hussein's regime, the supposed target of sanctions, remained unharmed.
The suffering the Iraqi people had to endure during that dark period may not have been forgotten so soon.
The attack might have also been intended to try to stop any greater UN presence in Iraq, especially a peace-keeping force.
But whatever the motives, one thing is sure - the bombing is a huge blow for UN operations in Iraq and for those who want a much bigger UN role in the country.
Discussions are currently ongoing in New York about how to increase the UN role.
But if the Iraqi resistance continues to target the UN itself, the organisation may become part of the problem rather than part of the solution.