Iraqi officials say bombings and other attacks have killed at least 50 people and wounded 160 others in mainly Shi'ite areas of the capital, Baghdad.
The violence Tuesday comes on the eve of the 10th anniversary of the U.S.-led invasion, and a month before Iraq is set to hold its first elections in three years.
The prime minister's office announced the April 20 election will be delayed by up to six months in Anbar and Ninevah provinces, because of threats and the killing of several candidates.
The bombs Tuesday struck in multiple Baghdad neighborhoods, including Sadr City and near the heavily fortified Green Zone where several Western embassies are located.
There was no immediate claim of responsibility. Sunni Muslim militants in Iraq frequently attack the country's majority Shi'ites to inflame sectarian tensions and undermine the Shi'ite-led government.