A suicide bomber disguised in a woman's burqa has exploded in a crowded bazaar in western Afghanistan, killing 18 police and civilians.

Another 22 people were wounded by the blast, which happened near a police station in the Del Aram district of Farah province as police were inspecting vehicles on the road.

Provincial governor Rohul Amin says the bomber was wearing an all-enveloping burqa robe commonly worn by Afghan women.

President Hamid Karzai condemned the attack, saying it was obscene for a bomber to use such a disguise.

A Taliban spokesman claimed responsibility for the attack.

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