A provincial police spokesman said the Monday robbery occurred at the Kabul Bank branch in Mazar-e-Sharif, the capital of Balk province, Indo-Asian News Service reported.
"This morning when the staff of the bank came to their office, they found six beheaded bodies of the guards that were locked inside a room," Sherjan Durani said.
Officials suspect that an insider was involved, as the guards' food had been poisoned beforehand, the BBC reported.
"It has the hallmark of an inside job. How do you poison the food of guards without someone inside?'' a senior security officer said.
Abdul Rauf Taj, deputy police chief of Mazar-e-Sharif, said no militant involvement was suspected.
"This is a criminal matter," he said.