At least 59 people have been killed in a suicide attack on an army recruitment centre in Baghdad, officials say.
More than 100 were reported to have been injured in the bombing, in the centre of the Iraqi capital.
The attack comes as the US prepares to end combat operations in Iraq by the end of this month.
It also comes a day after the bloc that won the most seats in March's parliamentary election suspended talks on forming a coalition government.
Violence in Iraq is down from the peak seen during the sectarian conflict in 2006-2007, although the number of civilian deaths rose sharply in July.
Almost daily attacks on Iraqi forces and traffic police in Baghdad and Anbar province, west of the capital, killed some 30 people in the first two weeks of August.
Desperate for jobs
The BBC's Hugh Sykes in Baghdad says that a suicide bomber walked up to the army recruitment centre where hundreds of people had been queuing for hours - some since Monday evening.
Unemployment in Iraq is running high and people are desperate for jobs.
The attack happened in a busy area close to one of the city's main bus stations, our correspondent says, adding that the streets would have been full of people early in the morning, making it easy for a suicide bomber to pass unnoticed.
Severed limbs were strewn across the street, which troops cordoned off as Iraqis turned up to look for relatives.
"I saw dozens of people lying on the ground, some of them were on fire. Others were running with blood pouring out," Ahmed Kadhim, a 19-year-old recruit, told the AFP news agency.
The site of the attack used to be the defence ministry during the rule of former President Saddam Hussein. It was converted into an army base and recruitment centre following the US-led invasion in 2003.
Some soldiers were reported to be among the victims on Tuesday. Three men were injured when two small bombs exploded last week at the same site.
There was no immediate claim of responsibility, although our correspondent says suspicion will fall on al-Qaeda in Iraq.
After a long lull, it has been much more active recently, possibly to coincide with what the Americans are calling the end of their combat operations in Iraq on 31 August, he adds.
The recruitment centre takes in about 250 recruits every week as the Iraqi authorities try to boost their armed forces. But there were more applicants than usual waiting because a recruitment drive was nearing its end, officials said.
The US is to reduce its forces in Iraq to 50,000 at the end of this month, and plans to withdraw all troops from the country by the end of 2011.
The 50,000 that will stay until next year will help train Iraqi forces and support counter-insurgency operations, although they will be combat-capable.
Iraq's top army officer recently questioned the timing of the pull-out, saying the country's military might not be ready to take control for another decade.
Meanwhile, Iraqi politics has remained deadlocked five months after national elections, with no new government yet in place.
On Monday, the al-Iraqiya bloc that narrowly won the most seats in March suspended talks with the second-placed Shia-led State of Law alliance of Prime Minister Nouri Maliki.
Al-Iraqiya, which is led by a former Prime Minister, Iyad Allawi, and says it is non-sectarian, was upset by a TV interview in which Mr Maliki said al-Iraqiya represented the Sunnis of Iraq.
Mr Allawi's alliance includes Vice-President Tariq al-Hashemi, a Sunni Arab, and senior Sunni politician Saleh al-Mutlaq.