Iraq's al-Qaida branch has claimed responsibility for the wave of bombings and other attacks that killed dozens in Baghdad and across the country the day before, The Associated Press reported.

The Islamic State of Iraq says it targeted security forces and government officials in "revenge for the elimination and torture campaigns that Sunni men and women face in the prisons of Baghdad and other cities."

The daylong series of attacks in 12 cities across Iraq killed 55 and wounded 225 people. The al-Qaida claim was posted on militant websites late Thursday, Feb 23.

In the past two months since the American military pulled out of Iraq, al-Qaida and other Sunni militants have stepped up attacks on Shiites, raising concern of a new surge in sectarian violence.