Chardara was secure, fierce fighting continued throughout the following days. A blow was dealt to the opposition forces by the killing of Taliban leader Mullah Ahsanullah on December 16. In January 2010, the United States and Germany agreed to increase their efforts in Kunduz by raising troop and civilian numbers to 6,000. After the successful advance into Chardara in late December the next stage of the offensive was launched on January 28. 500 German soldiers from two infantry battalions and 120 Afghan troops advanced across country and set up numerous permanent checkpoints, road blocks and heavily fortified observation posts; by the end of January, the coalition's presence took on an air of permanence, with a strong forward operating base and a net of outposts. Trying to stop the Germans from further construction work, nine insurgents were killed in action. A very serious situation unfolded during a firefight on February 5 when a routed group of Taliban in the process of being chased-down by German light infantry hid in a crowd of villagers, leading not only to their deaths but also to civilian casualties. Four days later an Afghan night patrol mistook a German patrol for opposing forces and opened fire. US special forces killed one insurgent and captured two more while searching for a Taliban commander in the far east of Afghanistan. On February 17, six insurgents were killed in clashes with German troops and 25 insurgents surrendered on February 22. Several insurgents were eliminated during clashes in the first two weeks of March. Again, close air support and mortars were used. One German soldier was wounded in action on March 5. Two Swedish officers were killed in action. Engagements followed throughout the next weeks, and on March 24 a contracted helicopter carrying ISAF-troops was shot down by insurgents. The largest battle yet since the fall of Kunduz to anti-Taliban forces in 2001 took place on April 2, the year's Good Friday, in the form of an attack by 200 insurgents. A platoon of 2nd Company, 373rd Airborne Battalion was caught in the open after a roadside bomb struck their patrol in the village of Isa Khel; simultaneously, the troops manning a nearby base situated in an Afghan police station came under fire as well. During nine hours of intense fighting, 20 soldiers out of the 36 strong German platoon trapped in Isa Khel were killed or wounded in action.