Dozens of people were injured in the mid-morning blast outside the Iraqi interior ministry.
The ministry has been frequently targeted in the past and is heavily guarded. At least eight policemen are reported to be among the fatalities.
It comes a day after at least 47 people were killed in a series of attacks across Iraq.
Insurgents have carried out almost daily attacks against Iraqi and coalition targets since the US-led invasion of Iraq in March 2003. Thousands of Iraqis have died in apparently sectarian attacks in the past four months alone.
The latest attacks undermined Iraqi Prime Minister Nuri al-Maliki's claim on Sunday that the security situation in Iraq was improving.
"The violence is on the decrease, and our security ability is increasing," Mr Maliki told CNN.
The bomber struck as UK Defence Minister Des Brown was in Baghdad for talks with Iraqi officials.
After meeting Iraqi Defence Minister Abdul-Qader Mohammed Jassim al-Mifarji, Mr Brown said Iraq was moving forward.
"Each time I come, I see more progress," he said.
Meanwhile, five US soldiers were killed in two separate bomb attacks in Iraq on Sunday afternoon, the US military said.
Four soldiers died when a roadside bomb hit their vehicle north of Baghdad, a military statement said.
A fifth soldier was killed when a roadside bomb struck his vehicle in the west of the capital.
Güncelleme Tarihi: 20 Eylül 2018, 18:16