At least 56 people were killed on Tuesday morning when a suicide bomber blew himself up outside an Iraqi army recruiting centre in Baghdad, officials were quoted by local media as saying.
The blast, which appeared to be targeting soldiers, police and new or potential recruits, also injured some 100 people.
According to witnesses, the centre had been open for the last week and the final day of recruitment was scheduled for Wednesday, causing a larger than usual number of people to be in the location at the time of the attack.
Security forces have increasingly been coming under attack from insurgents in recent months as the US starts to wind down its presence in Iraq.
The US military, which led the invasion in 2003, remains on track for ending major combat operations in Iraq by the end of this month and reducing its presence to about 50,000 soldiers. All US forces are scheduled to be out of Iraq by the end of 2011, the White House has confirmed.