Militants have carried out a number of attacks on cafes in recent weeks, especially during the Muslim holy month of Ramadan, when many Iraqis went to cafes after breaking their daytime fast.
This Ramadan, which ended last week, was one of the deadliest for Iraq in years, with more than 800 people killed in attacks.
The bomber struck a cafe in the town of Balad at around 6:30 pm (1530 GMT) today, also wounding more than 35 people, municipal council chief Faris Jaafar said.
"The Islamic State mobilised... In Baghdad and the southern states and others to convey a quick message of deterrence on the third day of Eid al-Fitr," the group said, referring to the holiday marking the end of Ramadan.
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"They (Shiites) will not dream of security during night or day, during Eid or other" days, it said.
The attack also came just weeks after assaults on prisons near Baghdad, also claimed by the Al-Qaeda front group, freed hundreds of prisoners including leading militants.
Analysts, as well as global police organisation Interpol, had warned that the jailbreaks could lead to a rise in attacks, as the escapees were said to include senior Al-Qaeda militants.
Violence in Iraq has increased markedly this year, with analysts saying the upsurge is driven by anger among the Sunni Arab minority that the Shiite-led government has failed to address, despite months of protests.
With the latest violence, attacks in Iraq have killed 3,396 people since the beginning of the year, according to figures compiled by AFP -- an average of 15 people killed each day.
But to the dismay of ordinary Iraqis, they have failed to stop the bloodshed.