The U.N. figures released on Thursday underscore concerns that security is quickly deteriorating in Iraq, where violence spiked in the last part of April.
The UN says it recorded 712 people killed last month, including 117 members of the Iraqi security forces. The capital district of Baghdad was the worst affected.
Casualty tolls in Iraq can vary considerably, with official reports at times differing from accounts from local police and hospital officials. The Associated Press recorded more than 400 killed last month.
Iraq witnessed its deadliest bout of violence between 2006 and 2007, when the country was on the brink of civil war.