"The month of April was the deadliest since June 2008. A total of 712 people were killed and another 1,633 were wounded in acts of terrorism and acts of violence," a statement from the UN mission in Iraq said.
"Baghdad was the worst-affected governorate, with a total of 697 civilian casualties (211 killed, 486 injured), followed by Diyala, Salaheddin, Kirkuk, Nineveh and Anbar," the statement said.
A wave of violence began on April 23 when security forces moved on Sunni anti-government protesters near the town of Hawijah in north Iraq, sparking clashes in which 53 people were killed.
The late-April violence was the deadliest so far linked to protests that broke out in Sunni areas of Shiite-majority Iraq more than four months ago.
The Sunni protesters have called for the resignation of Prime Minister Nuri al-Maliki, a Shiite, and criticised authorities for allegedly targeting their community with wrongful detentions and accusations of involvement in terrorism.