At least 51 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.

A significant and symbolic moment is fast approaching in Iraq, with the official end of the US combat mission there. Against that background, a very deliberate and devastating event like this was - in many ways - entirely predictable.

While US commanders insist they've battered the militant groups, they acknowledge that they are still capable of mounting significant attacks. But how frequently, and with what impact?

This latest incident only underlines the fact that Iraq remains far messier and more fragile than Washington would like. At the same time, America's ability to influence events is diminishing.

The 50,000 US troops that are remaining will officially be there only in a support and advisory role. But US special forces are also staying on, and a key question is how much pressure they'll be under to step in again militarily if the security situation deteriorates further.

The attack happened in a busy area close to one of the city's main bus stations, our correspondent says, adding that the streets are full of people early in the morning, making it easy for a suicide bomber to pass unnoticed.

Severed limbs could be seen in the street, which troops cordoned off as Iraqis turned up to look for relatives.

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 of Iraq in 2003.

Some soldiers were reported to be among the victims of Tuesday's attack. 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.

Political uncertainty

The recruitment centre takes in about 250 recruits every week as the Iraqi authorities try to boost their armed forces.

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 al-Maliki.

Al-Iraqiya, which is led by 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.

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