Right wing US presidential challenger Rick Santorum has launched a witty web ad to counter some of the negative attack ads sent his way by his main challenger, Mitt Romney.

A series of negative attack ads have already brought down Romney’s previous challenger, Newt Gingrich, but now Santorum is looking to turn the tables with a witty counter pitch.

Already the ad has proved to be a YouTube hit with a Mitt Romney lookalike taking centre stage as “Rombo”. Touting an automatic weapon he proceeds to take aim at a Santorum cut out, firing shot after shot of mud at his opponent – every one of which misses.

A narrator intones: “This time, Romney's firing his mud at Rick Santorum. Romney and his Super Pac have spent a staggering $20m brutally attacking fellow Republicans.

“In the end, Mitt Romney's ugly attacks are going to backfire”, thenarrator concludes, as Romney’s gun backfires splattering him with mud.