The British Museum is guarding a precious artefact that was looted from Syria, in the hope of returning it when the country is stable.
Director Neil MacGregor told The Times the museum was trying to protect antiquities taken from conflict zones.
And he called on the government to sign up to an international convention to protect cultural artefacts.
"We are playing a significant part in holding objects that have been illegally exported," he said.
"We did that in Afghanistan and are now returning them. We are holding an object we know was illegally removed from Syria and one day it will go back."
The destruction of museums, artefacts and archaeological sites amidst the Syrian conflict has been called "the worst cultural disaster since the Second World War".