Brussels, Aug 18 : The North Atlantic Treaty Organization (NATO) should make an honest assessment of what led to the "swift and sudden" collapse of the Afghan government and armed forces against the Taliban, NATO Secretary-General Jens Stoltenberg said on Tuesday. "The big question we have to ask and understand in a clear-eyed way is: why didn't the forces we trained, and equipped, and supported over so many years, why were they not able to stand up against the Taliban in a stronger and better way than they did?" Stoltenberg said at a press conference after a special meeting of NATO ambassadors to discuss the situation in Afghanistan, Xinhua news agency reported. "What we have seen in the last few weeks was a military and political collapse at a speed which had not been anticipated ... It was a surprise, the speed of collapse, and how swiftly that happened," he added. The NATO chief said that lessons will need to be learned, but at the moment the priority is to evacuate as many people as possible from Afghanistan. This includes NATO's own personnel, but also locals that have helped them, and people in vulnerable situations. Allies are sending more planes to Afghanistan to assist people in leaving the country, Stoltenberg said, and an airbridge is also being built for this purpose. He added that about 800 civilian personnel from NATO countries have remained behind in Afghanistan to keep Kabul airport running. Stoltenberg said that international terrorism remains a challenge and a threat in many places in the world. "Therefore, NATO needs to stay vigilant, to stay at the forefront of the fight against international terrorism. But there are lessons that need to be learned from Afghanistan, and we will do that." The NATO chief also urged the Taliban to allow those who wish to leave to do so, and keep roads and border crossings open. Also on Tuesday, German President Frank-Walter Steinmeier said that the images of desperation at Kabul airport were "shameful for the political West." "The failure of the years-long efforts to build a stable, viable community in Afghanistan raises fundamental questions about the past and future of our foreign policy and military engagement," he said. /IANS