BAGHDAD, Iraq, July 18 — An average of more than 100 civilians per day were killed in Iraq last month, the United Nations reported Tuesday, registering what appears to be the highest official monthly tally of violent deaths since the fall of Baghdad.

The death toll, drawn from Iraqi government agencies, was the most precise measurement of civilian deaths provided by any government organization since the invasion and represented a substantial increase over the figures in daily news media reports.

Contributing to the trend cited by the United Nations, a suicide car bomber killed at least 53 people and wounded at least 105 in the holy Shiite city of Kufa on Tuesday after he lured a throng of day laborers to his van with the offer of work.

The attack, one of the bloodiest this year, struck at the heart of Shiite Islam — Kufa is a stronghold of the powerful Shiite cleric Moktada al-Sadr and the site of a major shrine — and aggravated sectarian fury.