The male tourists were discovered inside the Banteay Kdei temple at the world heritage site on Thursday, Chau Sun Kerya, spokeswoman for the Apsara Authority -- the government agency managing the Angkor complex -- told AFP.
"The temple is a worship site and their behaviour is inappropriate. They were nude," she said.
Keat Bunthan, a senior heritage police official in northwestern Siem Reap province, confirmed the nationalities of the arrested and said many Cambodians would be offended by the tourists' actions.
"Their activities affect our culture. Nobody should take nude pictures at ancient temples," he told AFP.
The three were all in their early 20s, according to passport details released by the Cambodian authorities.
The Apsara Authority said in a statement that the three tourists have "admitted they really made a mistake by taking nude pictures".
The agency added Cambodian police were building a case against them and that they faced two possible charges.
The first -- public exposure -- is punishable by up to six months in prison and a maximum $120 fine while a second charge of making pornography could see the trio jailed for up to a year and fined $500.
The tourists were caught just days after a series of photos of Asian women posing nude at ancient Cambodian temples went viral online and outraged officials.
The Angkor Archaeological Park, a world heritage site, contains the remains of the different capitals of the Khmer Empire, dating from the 9th to the 15th century and is Cambodia's most popular tourist destination.