Suspected militants torched a column of trucks carrying military supplies just south of the Afghan capital on Tuesday and killed two NATO troops in the turbulent south and east. The attacks demonstrated the limited gains from the costly six-year effort to stabilize and bring security to Afghanistan, which is drawing in ever-larger numbers of NATO troops. German defense officials said Tuesday that they plan to increase the number of their troops in Afghanistan by 1,000 this fall. There are currently around 60,000 foreign troops in the country. Afghan officials said an unknown number of men riding motorcycles and armed with guns and rockets attacked the supply convoy near Saydabad, a town in Wardak province about 40 miles (70 kilometers) from Kabul.