US presidential hopeful Newt Gingrich has criticized President Barack Obama for issuing an apology to Afghan authorities over the burning of copies of the Koran at a military base. \"It is an outrage that on the day an Afghan soldier murders two American troops, President Obama is the one apologizing,\" the Republican candidate said in his Twitter account on Thursday. The burned copies of Islam’s holy book were found in a garbage pit on a US air field. The incident sparked outrage and violent protests across Afghanistan which led to the deaths of 14 people, including two US soldiers. President Obama has sent an apology letter to the Afghan leader Hamid Karzai reading: “I convey my deep sympathies and ask you and the people to accept my deep apologies.”   Campaigning in Washington state, Gingrich said that it is Karzai who owes the US an apology for the shootings and that the Afghans “do not deserve the apology of the United States,” the Associated Press reports.