(VOV) – US President Barack Obama on Friday sent a letter of apology to the Afghan Government for the burning of copies of the Muslim holy book at a US military base in the country. In the leter, Obama expressed his "deep regret for the reported incident" adding that the U.S. "will take the appropriate steps to avoid any recurrence, to include holding accountable those responsible". John Allen, commander of U.S. forces in Afghanistan said he has asked a joint investigation into the burning with Afghanistan in a transparent spirit to prevent possible cases.