Gen. Stanley McChrystal, a four-star American general with a long history in special operations, was to take charge of US and NATO troops in Afghanistan on Monday, a change of command the Pentagon hopes will turn the tide in the eight-year war. McChrystal is scheduled to take command from Gen. David McKiernan during a low-key ceremony at the heavily fortified headquarters of the NATO-led International Security Assistance Force in central Kabul. McKiernan was fired last month by Defense Secretary Robert Gates halfway through his two-year assignment. An outgoing general typically hands off command to his replacement during a ceremony, but McKiernan quietly left the country earlier this month. McChrystal, a former commanding general of the Joint Special Operations Command, is expected to bring a more unconventional approach to a war that has turned increasingly violent in the last three years. He will command the largest international force ever in Afghanistan. A record 56,000 U.S. troops are in the country, alongside 32,000 forces from 41 other countries. American troops have poured into Helmand province over the last several weeks in an effort to stamp out an insurgency that has a strong hold in the world's largest opium-poppy growing region. McChrystal met Sunday with President Hamid Karzai, who warned the American general that the ''most important element of the mission'' is the protection of Afghan civilians. Civilian casualties during military operations has long been a point of friction between Karzai and the U.S. The most contentious civilian deaths in U.S. military operations in recent years have involved U.S. Special Operations Forces, which McChrystal used to command. He has pledged to review U.S. and allied operating procedures with an eye toward minimizing civilian deaths.