Al-Qaida's Iraqi affiliate says it carried out the wave of attacks Tuesday that killed around 60 people, mainly in Shi'ite areas in and around the capital, Baghdad.
The Islamic State of Iraq posted a statement on jihadist forums Wednesday claiming responsibility, saying the attacks were a "first stage" that will be followed by "revenge."
The more than a dozen bombs that exploded across Baghdad during the Tuesday morning rush hour also wounded more than 160 people. Several bombings also were reported in towns north and south of the city.
It was one of Iraq's deadliest days in months, and came on the eve of the 10th anniversary of the U.S.-led invasion of Iraq.
U.S. President Barack Obama issued a statement Tuesday for the anniversary, paying tribute to the 1.5 million Americans who served "in one of our nation's longest wars," which ended with a U.S. withdrawal in December 2011.
Obama said the 4,475 U.S. military personnel who died "made the ultimate sacrifice to give the Iraqi people an opportunity to forge their own future after many years of hardship."
The Iraqi government said Tuesday it is postponing local elections scheduled for next month in the provinces of Anbar and Ninevah by up to six months, because of security threats to electoral workers and candidates.
Voting in Iraq's other provinces is due to go ahead as planned on April 20.