The findings on Sunday, gathered by comparing satellite imagery of the city collected in July 2014 to imagery collected in December, reveal that nearly 1,500 buildings have been completely destroyed, the report said.
The Islamic State in Iraq and the Levant (ISIL) group overran Ramadi, capital of Anbar province, in May after months of clashes with Iraqi government forces. Last month government forces retook the city's western and central districts.
"The kind of damage that happened in Ramadi is incomparable to what we saw in Tikrit," said Lise Grande, the UN's deputy special representative to Iraq, referring to the last major city that forces aligned with the Iraqi government took back from ISIL control. The extent of the damage in Ramadi, she says, raises concerns about reconstruction, the Associated Press reported.
Grande emphasized the report was preliminary as UN teams have not yet been able to access Ramadi, 70 miles (115 kilometers) west of Baghdad, on the ground.
While members of the US-led coalition to fight ISIL have pledged more than $50 million to Iraqi reconstruction, Iraqi and coalition officials estimate that rebuilding Ramadi alone could cost hundreds of millions of dollars.
ISIL swept into Iraq in the summer of 2014, overrunning nearly a third of the country including Iraq's second largest city of Mosul.
Since then, Kurdish forces in the north and fighters aligned with the central government in the country's western and central provinces have slowly clawed back some territory from the militant group.
But months of violence and the scorched earth practices ISIL employs upon retreat have left much of the reclaimed territory uninhabitable. As of November the UN estimated that 3 million Iraqis remained displaced by violence.