Kabul, Afghanistan (CNN) -- Afghan rage over the burning of Qurans by NATO troops continued Thursday even after a President Barack Obama apologized for the "error." Afghanistan erupted in violent demonstrations after the troops burned the Islamic religious material at the beginning of the week. Two American troops were killed Thursday by a man wearing an Afghan National Army uniform, a U.S. official said, asking not to be named discussing casualties. The gunman is thought to have been acting in conjunction with a protest outside the base, the official said. In a letter delivered to Afghan President Hamid Karzai, Obama called the act "inadvertent," Karzai's office and National Security Council spokesman Tommy Vietor said Thursday.
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NEW: Gingrich wants apology from Afghanistan for U.S. troop deaths
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Two American troops were killed Thursday by man in Afghan army uniform
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An Afghan religious scholar says American "carelessness "was "a crime"
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Two people also die and nine, including Americans, are injured in a protest, an official says
"Any disciplinary action, if deemed warranted, will be taken by @placeholder authorities after a thorough review of the facts pursuant to all law and regulation and in accordance with due process."