Almost all of the contents of Iraq's national library and archives are reported to have been destroyed by fire, meaning the loss of priceless records of the country's history.
Many of Baghdad's museums have also been looted
The library, in central Baghdad, housed several rare volumes, including entire royal court records and files from the period when Iraq was part of the Ottoman Empire.
It is unclear who started the fires - though widespread looting has taken place in the Iraqi capital, with the city's museum also ransacked and many rare artefacts damaged, destroyed or stolen.
The US Secretary of State, Colin Powell, has pledged to recover and repair the antiquities looted from the city museum, amid criticism from heritage bodies that the damage should have been prevented.
A Western journalist - Robert Fisk of the Independent - reporting from the site of the library told the BBC that the whole building had been gutted, with handwritten documents from as far back as the 16th century - when Iraq was part of the Ottoman Empire - strewn on the ground.
A nearby Islamic library has also gone in up in flames, he said, destroying valuable literature including one of the oldest surviving copies of the Koran.
US-Iraqi joint patrols have now begun around the city in a bid to curb the violence.
It's too late, it's no use, it's no use
Archaeologist, Iraqi state board of
Several Shia religious leaders have appealed to the local population to return looted items, and say that some items had been returned and stashed in mosques for safekeeping.
"We will return them when we will have a democratic government," Shia cleric Sayyad Ali al-Shawki told the Associated Press news agency.
Mr Powell called the ravaged Baghdad museum "one of the great museums in the world" and said the US would take a leading role in restoring it.
Leading experts on Iraqi heritage will gather for an emergency meeting on Thursday to count the cost of the looting of the country's cultural sites.
'Recover and restore'
Mr Powell said the US would secure the museum and would work with organisations such as the European Union and the cultural arm of the United Nations, Unesco, in restoring it.
The US would "recover that which has been taken and also participate in restoring that which has been broken", he said.
But the loss and destruction already suffered has been described as "a disaster" by Unesco.
Iraq: The "cradle of civilisation"
The national museum was home to artefacts that dated back 10,000 years, from one of the world's earliest civilisations.
The development of writing, abstract counting, the wheel and agriculture were all charted in its exhibitions.
The collections from the Sumerian, Babylonian and Assyrian periods were particularly prized.
'History of mankind'
Despite Mr Powell's assurances, there are fears that many objects may have been be lost forever.
After the 1991 Gulf War, 4,000 pieces disappeared when regional museums were looted.
Donny George, archaeologist at the museum, said: "It was the leading collection of a... continuous history of mankind.
"And it's gone, and it's lost. If marines had started before, none of this would have
"It's too late, it's no use, it's no use."