At least two Turkish nationals and one Afghan were killed Saturday -- and two other Turkish nationals injured -- when an unidentified gunman opened fire on them in Kabul, according to a local police official.The attack occurred at about 7 p.m. local time in a Turkish Bazaar in central Kabul.The area was soon cordoned off by security forces, while the injured were taken to hospital.An employee of the company for which the slain Turks had worked told Anadolu Agency on condition of anonymity that the company's owner had been seriously injured in the attack and was currently in critical condition."They were visiting Afghanistan to explore possible investment opportunities," the employee said.The motive for the attack remains unclear.No militant groups, including the Taliban, have yet claimed responsibility for Saturday's attack.