'Stop this sick video game'.
Mr Howard said he was "appalled" by the game - which originated in America and is thought to have been distributed to many of Britain's 400 computer libraries.
As campaigners seeking a handgun ban after the Dunblane tragedy called for legislation to outlaw the games, Mr Howard pointed out: "It is a criminal offence for such games to be distributed if they haven't got a certificate.
"The police have powers to enforce this law and have our full support to do so."
Meanwhile pupils from the Dunblane school who survived the massacre earlier this year are to sing on a new recording of Bob Dylan's hit Knocking On Heaven's Door which will be released as part of the handgun ban campaign.