U.S. Republican presidential candidates on Sunday blasted President Barack Obama\'s Afghanistan policies, including his apology over the burning of Qurans by NATO troops. \"I think the president\'s made some enormous errors in the conduct of our mission there,\" Mitt Romney, former Massachusetts governor and long-time front-runner in the GOP nomination race, said on Fox News Sunday. Romney has repeatedly criticized the Obama administration on its Afghan policy, particularly its withdrawal plan which he said could potentially undermine the security gains the U.S. military achieved in the past years. Like many other Republicans, the former governor wasted no chance to blast Obama\'s recent apology to the Afghan people after the burning of Qurans by NATO troops sparked a wave of violence in the country. \"For us to be apologizing at a time like this is something which is very difficult for the American people to countenance,\" Romney said. Obama apologized on Thursday in a letter to Afghan President Hamid Karzai over the burning of Qurans at the U.S.-run Bagram Airbase near Kabul. The unprecedented anti-U.S. demonstrations in Afghanistan since Tuesday have resulted in over 30 deaths and more than 200 injuries, including four American servicemembers killed in apparent revenge attacks. Rick Santorum, Romney\'s currently most formidable rival in the GOP race, also expressed his opposition to the president\'s decision to apologize. \"There was nothing deliberately done wrong here,\" the former Pennsylvania senator said on ABC\'s This Week. \"To apologize for something that was not an intentional act is something that the President of the United States, in my opinion, should not have done.\"