The general chosen to lead US and NATO forces in Afghanistan warned on Tuesday that the war against insurgents could be lost unless civilian casualties were reduced. Lieutenant General Stanley McChrystal, nominated by President Barack Obama to take over as commander in Afghanistan, told a congressional hearing that civilian deaths from coalition operations risked inflaming public anger and undermining military advances on the battlefield. "If defeating an insurgent formation produces popular resentment, the victory is hollow and unsustainable," McChrystal said at his confirmation hearing. "This is a critical point. It may be the critical point. This is a struggle for the support of the Afghan people. "Our willingness to operate in ways that minimize casualties or damage -- even when doing so makes our task more difficult -- is essential to our credibility." Civilian casualties -- often from US air power -- have caused mounting popular outrage in Afghanistan and friction with the Kabul government, with US and Western officials worried about handing propaganda victories to their Taliban foes. President Hamid Karzai has demanded a halt in air strikes after one of the deadliest such incidents of the war in Bala Buluk, where his government says 140 civilians died earlier this month. McChrystal, named to replace General David McKiernan as the top commander in Afghanistan, vowed to make protecting civilian lives a top priority. Success in the conflict against insurgents should be measured not in the number of enemy killed but in "the number of Afghans shielded from violence," he said. McChrystal, who met with a mostly friendly reception from members of the Senate Armed Services Committee, is due to take over the helm at a pivotal moment in the Afghan war after Obama unveiled a new strategy and ordered more than 21,000 additional troops to bolster the US force. As a former special operations commander, McChrystal's elite troops carried out manhunts in Iraq that won him praise but human rights groups say his special forces lacked restraint in their interrogations of detainees. McChrystal did not face a tough grilling from senators over the issue, but acknowledged he had misgivings about harsh interrogation techniques that were approved by then-secretary of defense Donald Rumsfeld.