Iraq's May death toll announced
The figures showed 1,045 civilians and security personnel killed in May. That surpassed the 712 killed in April, the deadliest month recorded since June 2008.
More than half of those killed were in the capital district of Baghdad.
Tallies of Iraq casualties have long been the subject of debate, and the UN total is considerably higher than that reported by news agencies in the country.
The Associated Press counted at least 578 Iraqis killed in May, based on reports from Iraqi officials.
The UN says its totals are based on direct investigation and accounts from credible outside sources.