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A suicide bomber blew himself up as he walked alongside a political demonstration in Khost, Afghanistan Thursday, police said, killing at least 18 civilians in a moment of horror that was caught on video.

The bomber detonated a vest filled with explosives in the middle of a crowd that was calling for the removal of a provincial governor.

At least 64 others were injured in the blast — including an elected lawmaker in Afghanistan’s parliament, Humayun Humayun — according to provincial police chief, Gen. Faizullah Khan.

“We don't know who was behind the attack, but it is the work of the enemies of peace and stability of the country,” Khan told NBC News.

The attack happened at 9.45 a.m. local time, he said.

— Alastair Jamieson