KABUL, Afghanistan (CNN) -- A Briton and a South African, killed in Kabul Saturday, were shot by a security guard who then took his own life, an Afghan Interior Ministry official said Sunday.
The men were both employees of the Afghan branch of DHL, an international courier service. One served as director; the other as deputy director.
Both were killed when the guard opened fire as their vehicle approached the DHL office, located near the presidential palace in the capital, Interior Ministry spokesman Zemarai Bashary said.
The gunfire wounded two other guards before the attacker fatally shot himself in the neck, Bashary added. Watch more about the shootings »
"We can't say if he was recruited to do the job or there were some other issues," he said, adding that the investigation into the incident continues.
The guard had been working for about four years with a British-based security company that provides personnel to banks, international organizations and private companies operating in Afghanistan, Bashary said.
Officials arrested 13 people, including employees of DHL, after the shooting. But police released them after determining they were not involved.
Meanwhile, security companies in Afghanistan have been asked to provide a list of their employees to the government, said Alishah Ahmadzai, Kabul's deputy police chief.
The Afghan government says it is trying to regulate private security companies and has shut down several for operating illegally.
Bashary said 60 security firms were authorized to conduct business in Afghanistan , but hundreds of others continue to provide security without a license.
Earlier, the British Foreign Office said DHL had spoken to the men's relatives. But neither the British nor the South African government identified the victims.
DHL released a statement saying only that the 8:30 a.m. shooting killed two of its employees. The company said it is cooperating with police and will not be releasing further details at this time, the statement said.
"At this difficult time our thoughts are with the families, friends and colleagues of those who have lost their lives under such tragic circumstances," it said.
Journalist Farhad Peikar contributed to this report.
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