The extremist group has destroyed shrines, churches and precious manuscripts in Mosul, Tikrit and other areas of Iraq and excavated sites to sell objects abroad. UNESCO chief Irina Bokova has described the acts as "cultural cleansing".
In July IS rigged the Nabi Yunus shrine in the northern city of Mosul with explosives and blew it up. The shrine is revered by both Muslims and Christians. The radical group advocates a brutal and strict interpretation of Islam, and considers worshipping at graves to be tantamount to idolatry.
According to Baghdad museum director Qais Rashid there were explosions that destroyed buildings dating back thousands of years to the Assyrian era. Mr Rashid claimed "Assyrian tablets were stolen and were suddenly found in European cities", warning that the sale of such artefacts was being used to "finance terrorism".
"There are international mafias ... that inform Daesh of what can be sold," he stated, referring to an alternative name for IS. "The Mosul museum, the second most important in Iraq, suffered an attack from Daesh and they also attacked the staff from the museum," he said.
In another incident, "Daesh gathered over 1,500 manuscripts from convents and other holy places and burnt all of them in the middle of the city square," he added. Iraqi authorities have yet to put together a detailed list of what exactly has been destroyed or looted.
Ms Bokova said she had alerted all UNESCO member states, "as well as the main museums around the world and the art market, Interpol, the World Customs Organisation ... by calling for the utmost vigilance over objects that could come from the current looting of Iraqi heritage".
She added that UNESCO had handed over the geographical co-ordinates of all key heritage sites to countries engaged in air strikes over Iraq to fight IS, to prevent further damage.