"Parts of Afghan security forces fought bravely, but they were unable to secure the country because ultimately the Afghan political leadership failed to stand up to the Taliban and to achieve the peaceful solution that Afghans desperately wanted," Stoltenberg said. This was what caused "the tragedy we are witnessing today," he told reporters via videolink from Brussels. Following the US decision to withdraw from Afghanistan the allies faced a difficult choice, according to Stoltenberg. Allies knew that they risked allowing the Taliban to retake the country if they left or faced reprisal attacks and the need to re-engage in combat if they stayed, he said. The alliance had difficult questions to ask itself, Stoltenberg added. "Despite our considerable investment and sacrifice over two decades, the collapse was swift and sudden," he said. The NATO chief has called on the Taliban to allow those wishing to leave Afghanistan to do so in safety and called on the radical Islamist group to respect human rights. "The Taliban must respect and facilitate the safe departure of all those who wish to leave," Stoltenberg told reporters from Brussels. Kabul airport, borders and roads must be open, he said. Though the alliance itself no longer had any military personnel on the ground, it still had a civilian representation, which was assisting with evacuation efforts, he stressed. "We remain committed to completing evacuations including of Afghan colleagues as soon as possible," the alliance chief said, adding that allies would send additional aircraft. "A government that does not respect the fundamental rights of all Afghans and reinstates the reign of fear risks international isolation," Stoltenberg said, in a warning to the Taliban.