A Cambodian food stall began on Monday serving a thin, watery rice porridge that almost everyone had to eat during the 1970s rule of the Khmer Rouge, who were responsible for one of the worst genocides of the 20th century.

The owner of the small "Pol Pot regime porridge" shop in Siem Reap town said he wanted to offer the porridge as a reminder of the country's dark past.

About 1.8 million people were killed during the 1975-1979 rule of Pol Pot's ultra-communist Khmer Rouge, from torture, execution, disease and starvation after harvests failed.

Restaurant owner Tuon Tem, 49, said he lost nine relatives at that time and was offering the porridge to remind young people about how hard life was then.

"I had this idea to have young people, including my children, to know how hard it was," Tuon Tem, who is also a captain in the army, told Reuters by telephone.

Tuon Tem said he offered two plates of porridge, a modern version with fish, vegetables and rice and the Khmer Rouge style, a thin gruel with salt on the side, all for $1.5.

Customer Chin Ka Moniroth, 26, was not impressed with the dish, though he said the restaurant might attract young people, wanting to try something new.

"It's tasteless, it's just water and salt," Chin Ka Moniroth said.

Police were also not impressed with the restaurant, saying it could not use the name Pol Pot.

"He was a brutal killer," Siem Reap police chief Ho Vanny told Reuters. "This is not appropriate."

Tuon Tem said police had told him to remove the sign but he had not done so, not yet anyway.