A double car bombing killed at least 10 people and wounded 60 in a crowded market in the northern Iraqi city of Kirkuk torday.
The explosions in the predominantly Kurdish Rahim Awa district coincided with a surprise visit to the capital Baghdad by US Secretary of State Condoleezza Rice.
Several cars and shops were burnt out after the blast. Hospital officials said the condition of many of the wounded was life-threatening.
Iraqi officials fear violence may increase outside the capital Baghdad as US and Iraqi forces step up a crackdown on insurgents and militias in the city.
Some officials say militants are avoiding confrontation in Baghdad or may have left the city.
Ms Rice arrived in Baghdad as American and Iraqi troops made early gains in a new crackdown against militants.
"The Baghdad security plan is just beginning to unfold and I think it is important to realise it was not ever intended to be a single day, but to ramp up over time," she told reporters.
She added it was important for the Iraqi authorities to use the "breathing space" well.
Ms Rice who will meet various officials during her Iraq visit, who later travel Jerusalem, where she is scheduled to meet Israeli Prime Minister Ehud Olmert and Palestinian President Mahmoud Abbas on Monday.
Her visit to Baghdad comes a day after the US House of Representatives denounced President George W Bush's decision to send more troops to help with the offensive.
The move was a symbolic challenge to Mr Bush's unpopular war. US and Iraqi forces sweeping through Baghdad have encountered little resistance to an operation seen as a final effort to quell violence threatening to tear Iraq apart.
Shi'ite officials have warned that failure of Operation Imposing Law in Baghdad could mean a collapse of the Shi'ite-led government of Prime Minister Nuri al-Maliki.