The bomber in the northern Iraqi oil hub of Kirkuk exploded his car at the entrance to the Bab al-Aswad bank in the south of the city on Thursday.
Adel Zine al-Abidin, a local police chief, said the blast occurred just as Iraqi soldiers were waiting to collect their salaries.
A large part of the bank building, two army vehicles and several nearby shops were set on fire by the explosion.
In a separate incident earlier in the day, 10 people were killed in a suicide attack in Mosul
Abdel Karim Khalaf, an interior ministry spokesman, said one officer died along with nine civilians. Of the 14 people wounded, eight were police.
Hospital sources said the death toll could rise.
The blast was heard across Mosul, 390km north of Baghdad. The city has witnessed a recent escalation of violence.
Sunni Arab fighters battling US troops and the Shia- led government in Baghdad frequently attack Iraq's security forces.
The US military has said that a joint operation with Iraqi forces in the capital has "not met our overall expectations," as attacks rose by 22 per cent during the past three weeks.
Major General William Caldwell, the US military spokesman, said the rise in attacks was "disheartening", and that the Americans are now working with the Iraqi authorities to "refocus" security.
"In Baghdad, Operation Together Forward has made a difference in the focus areas, but has not met our overall expectations in sustaining a reduction in the level of violence," Caldwell said.
About 12,000 extra US and Iraqi troops were deployed on August 7 to secure the capital.
The US military has also announced the death of two more soldiers in Iraq.
One of the US soldiers was killed in the city of Ramadi while the other was killed in Baghdad when his patrol came under attack.