The group of nine men broke into the Egyptian Museum, which is on the edge of Tahrir Square, the epicentre of protests, searching for gold.
They broke into ten cases to take figurines. When they discovered that the figures did not contain gold, they dropped them and the items broke. They then seized two skulls of the 2,000-year-old mummies and fled.
Dr Zahi Hawass, the director of the museum, said: "Demonstrators in collaboration with security forces stopped the thieves and returned the relics to the museum – but they were already damaged. Only their heads were intact."
Egyptologists described the smashing of the irreplaceable artefacts as "devastating".
"It's is absolutely appalling," said Robert Connolly, an anthropologist and Egyptologist from the University of Liverpool. "If Egyptians are looting their own heritage then it is truly terrible. [..]