The director and deputy of the international courier service DHL in Afghanistan, both foreign men, were shot dead outside their office in central Kabul Saturday morning. The police said the assailant was one of their security guards.
The police said the guard then shot himself. Two other Afghans were seriously wounded in the shooting, the police said.
The British Foreign Office said one Briton and one South African were killed in the attack, but did not immediately release their names.
Gen. Ali Shah Ahmadzai, the deputy police chief of Kabul, called the shooting "an internal issue of their office."
Other police officials did not rule out a connection to insurgents.
"This was a terrorist-style attack," Mirza Mohammed Yarmand, the chief of the criminal investigations department, said Saturday, adding that the guard had nothing in his pockets and no cell phone, a precaution suicide bombers often take.
Monday, British aid worker Gayle Williams, 34, was gunned down in western Kabul, which further raised security concerns for the thousands of foreign nationals in the capital.
The shooting Saturday took place about 11 a.m. at a busy intersection opposite the Iranian Embassy and near several other embassy compounds.
Taliban spokesman Zabiullah Mujaheddenied that the movement was responsible for the attack.