A group that claims to be affiliated with al-Qaeda posted on its website Friday that it was behind this week's bombings in Baghdad, which killed at least 64 people in one of the bloodiest series of attacks in months, DPA reported.
The group, which calls itself the Islamic State of Iraq, said the bombings were a "revenge" on Shiite "transgressions" and "impurities." The group said that Shiite scholars have "cursed and insulted" the Prophet Muhammad and his followers.
They said the attack was just the beginning and vowed more would follow.
Despite the claim of responsibility, there was so far no official confirmation in Baghdad that the group was behind Tuesday's bombings which injured at least 360 people.
The series of around 21 explosions from car bombs, suicide bombers and mortar attacks targeted mostly Shiite neighbourhoods in Baghdad.
Just two days earlier, at least 52 people had been killed and more than 75 injured in the capital when militants who claimed to be members of the Islamic State of Iraq seized a Christian church.
"These attacks are a clear attempt at inciting sectarian strife and disrupting national unity," Iraqi Premier Nuri al-Maliki said shortly after both attacks.
Earlier in the week, Iraqi police arrested 96 people in a large raid on a northern Iraqi town, as people elsewhere in the country buried and mourned the dead from the recent wave of violence.
Police did not immediately identify those arrested or link the raid to any specific recent attack.