Survivors of the Khmer Rouge hit out at Pokemon GO players on Wednesday after they flocked to one of the regime's notorious prisons -- now a museum to Cambodia's brutal genocide -- to catch digital monsters.

The mobile app was made available in Cambodia on Saturday alongside a host of other Southeast Asian nations, with fans flocking to well known landmarks in recent days.

But the game -- which encourages users to hit the pavements in search of the virtual creatures -- has sparked anger after players appeared at Tuol Sleng prison, where up to 15,000 people were sent to their deaths during the Khmer Rouge's 1975-79 rule.

"It is an insulting act to the souls of the victims who died at there," Bou Meng, 76, one of a handful survivors from Tuol Sleng, told AFP.

"It is a place of suffering. It is not appropriate to play the game there," he said, calling for museum to be excluded from the game's maps.

Youk Chhang, director of the Documentation Center of Cambodia, which researches the Khmer Rouge atrocities, echoed Bou Meng's call.

The museum is "not a shopping mall nor a playground to catch Pokemon. It is a grave site," he said.

Chhay Visoth, the director of the Tuol Sleng Genocide Museum, confirmed some visitors had played Pokemon Go inside the prison.

He added that the museum had stepped up measures to stop people playing the game there because the site was "a sad place" of reflection.

Since its global launch, Pokemon Go has sparked a worldwide frenzy among users who have taken to the streets with their smartphones.

The viral game uses satellite locations, graphics and camera capabilities to overlay cartoon monsters on real-world settings, challenging players to capture and train the creatures for battles.

While it has been praised as a fun way to get people outdoors, it has also attracted safety and security warnings.

It is not the first time players have turned up at sensitive historical sites.

A French World War I memorial has been removed from Pokemon Go following complaints about gamers gathering to do battle at a site containing the remains of 130,000 soldiers.