A suicide bomber in a four-wheel-drive vehicle blew up his cache of explosives on Tuesday morning in Herat province in western Afghanistan, killing nine people and wounding 21, authorities said.

The attacker struck as people were gathered outside a district headquarters building, waiting to go inside to see government officials about various business matters, said Nasar Ahmad Popul, the chief of the province’s Guzara district.

“When a suicide bomber tried to enter the district headquarters, he was stopped by the police but then he detonated his explosives right at the gate,” said Popul, who was inside the building at the time of the blast. “The explosion was so strong, there are casualties among police and civilians.”

Noor Khan Nekzad, a spokesman for the provincial police chief, said nine people were killed, three Afghan police and six civilians. Another 21 people were wounded, most of them civilians, he said.

The responsibility for nearly all of Herat province has been transferred, or is in the process of being transferred, from NATO troops to Afghan forces.

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