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.

“The vehicle wasn’t armored and didn’t have any military markings,” he said, adding that the women had been working at the airport for a number of years.

The women killed were responsible for searching females transiting through the airport and their belongings.

“Police have begun a search operation to look for the perpetrators,” said Samim Khpalwak, the spokesman for the Kandahar province’s governor.

Constellis Group communications manager Katy Pultz said the company wasn’t aware of any threats to its female staff members, and that it is assisting Afghan authorities while conducting its own separate investigation into the attack.