The Taliban confirmed the move with a statement along with an interview with Abdulhai posted on the group's website, Khaama Press reported Thursday.
The reason Abdulhai and two of his bodyguards defected to the group was unclear.
Abdulhai is thought to be the highest-ranking civilian official ever to join the Taliban, the BBC said. He served as a senator from 2004 to 2008 and later was made a district governor in Sar-e-Pol.
Local government officials said they could not confirm the defection.
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