The bus, which was said to be carrying Nepalese security guards, was on a road to the eastern city of Jalalabad.
The attacker, who was on foot, waited for the bus as it left a compound, police said.
A Taliban spokesman claimed responsibility for the attack, the first since the start of the holy month of Ramadan.
“The suicide bomber targeted a minibus of security guards of a foreign company, right now we are working to identify the nationalities of the victims,” Interior Ministry spokesman Sediq Sediqqi told the Associated Press.
More than two dozen ambulances were present at the scene, according to an AFP witness.
The incident follows a suicide attack on a bus near Kabul last month and an attack on a court in Ghazni in June. Both attacks were claimed by the Taliban in revenge for the execution of six prisoners.
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Image courtesy of Reuters