KABUL—Unknown gunmen killed five female security employees and their driver on their way to work at Kandahar airport in south Afghanistan, officials said, the latest episode of violence against women in the country’s security sector.

The women were employees of Olive Group, a foreign company that is responsible for securing the airport, in Afghanistan’s second largest city. It is part of Constellis Group, which includes the firm formerly known as Blackwater.

No group immediately claimed responsibility for Saturday’s killings. The Taliban, who have previously carried out attacks against female police and government workers, denied any role.

The gunmen ambushed the women’s vehicle when it stopped to pick up the fifth employee, said Ahmadullah Faizi, the airport’s director.