BAGHDAD — An al-Qaida-affiliated group in Iraq claimed responsibility on Wednesday for bloody attacks that killed dozens of people across the country a day earlier.

In a statement posted on a militant website, the Islamic State of Iraq said the car bombs and other explosions came to avenge the executions and "massacres" of convicted Sunni inmates held in Iraqi prisons.

Most of the nearly 20 attacks on Tuesday, the eve of the 10th anniversary of the 2003 U.S.-led invasion, targeted Shiite areas in Baghdad.