Robots are on patrol in IRAQ, and they are currently armed (i.e carrying loaded machine guns). They are not actually autonomous, but remote controlled, so I am a bit ambivalent about really calling them robots. They do carry M249 SAW machine guns made by Fabrique Nationale US (the US arm of a Belgian company [provenance corrected thanks to a comment, below]). They also have the capacity to carry grenade launchers and other product-dispensing apparatus. The robot does not seem to be the most stable one I've seen, and it uses pretty conventional drive mechanisms, but it's obviously very robust. In many ways the actual robot technology itself seems somewhat dated compared to what the research community is working on, but the application in the field is almost unique. The vehicle is made by Foster-Miller, and is part of a package called SWORDS (Special Weapons Observation Reconnaissance Direct- action System). Foster Miller is a large company that has supplied robots such as this for bomb disposal (EOD) application for some time.
According to Foster Miller the robot was "... evaluated by the 5th Special Forces in Iraq and three systems have completed evaluation with the 3rd Infantry Division and [were] deployed to Iraq in 2007."
The M249 machine gun is fully automatic, has a maximum range of about 1000 meters (3281 feet). When loaded with the "preferred" ammunition of M855 Ball (whatever that means), it is suitable for use against light materiel targets and personnel. The military expects to use it in the near future to dispense deadly force. When this happens, it will be a dangerous precedent, but one that was obviously inevitable and which is a natural extension of existing technologies (such as drone aircraft).