An American man has been arrested after being found in a child sex brothel in Cambodia, where he allegedly gave a girl $100 a month.

Danny Pope was in a private room inside the massage parlor in capital Phnom Penh when officers raided the building on Saturday morning.

Police said they had been monitoring the brothel as well as the 59-year-old suspect, from Statesville, North Carolina, for two days before raiding the two-story property.

An orange sign outside the building advertises massages for 10,000 Cambodia Riel ($2.47) and says the shop is open 24 hours a day.

Five prostitutes - including three children - were discovered inside the building and taken into care.

Footage showed Pope - wearing a white shirt and with a grey mullet - being lead away and put onto a police motorcycle.

He was interviewed at the police station where he told officers that he had been giving one of the young girls '$100 a month for food and clothes'.

Asked if he had given money to any of the other children, he said 'no just her'.

It is not known if Pope was questioned about his social media profile, which shows him posing with different Asian children over a number of years.

Police took Pope, then wearing a black check shirt and black hat, back to the brothel named Srey Nean 871 and also back to his rented room on a police parade.

He has since been remanded in custody while police prepare the case to give to prosecutors.