BAGHDAD, Feb 10 (Reuters) - A new U.S. general took command of the American military in Iraq on Saturday, just days after an offensive began in Baghdad that aims to halt the country's slide into civil war. General David Petraeus, a veteran of two Iraq tours and a counter-insurgency expert, took over from General George Casey during a ceremony at a U.S. base near Baghdad's airport. Petraeus has urged that 21,500 extra American troops being sent to Iraq for the campaign be deployed as quickly as possible. Casey had been sceptical of troop increases.