"Roboguard", devised in Thailand, can shoot at will or wait for the order to fire from its human masters via the internet.

At present the machine, consisting of a handgun and a small video camera, is statically mounted on a directional platform.

But its inventor hopes to develop the device into a robot that can pursue a target on foot.

Pitikhate Sooraksa, of King Mongkut's Institute of Technology in Ladkrabang, Bangkok, told New Scientist magazine: "You could make it mobile, it could be designed as a walking system. We have the technology."

Fire when ready

The robot can be operated both manually and automatically.

In manual mode, the gun can be controlled from a computer anywhere in the world. A laser on top of the gun marks the target.

To operate automatically, Roboguard has infrared sensors that allow it to track people's movements.

When controlled over the internet, it has a password-protected "fire" command.

To test the robot's accuracy, Sooraksa pinned balloons to walls and took pot shots at them from a computer.

At present, Roboguard is equipped with an air pistol but Sooraksa says it would be simple to upgrade to a more powerful weapon, such as a machinegun.

Horrified reaction

The idea horrified British robotics experts.

"Things can always go wrong. We need to think about introducing laws like Asimov's, but even then robots will find ways to get round them," said Kevin Warwick, a cyberneticist at Reading University, UK.