RFE/RL's Tajik Service reports that Gaffor Mirzoyev faces 30 charges, including plotting to overthrow the government, murder, abuse of office, possession of illegal weapons, and fraud.
The trial is being held behind closed doors at the Supreme Court.
Mirzoyev's lawyer, Abdukayum Yusupov, says his client denies the charges and is insisting on an open trial.
Mirzoyev was arrested in 2004. An influential commander of pro-government forces during the civil war that raged from 1992 to 1997, Mirzoyev was a member of the President Rakhmonov's inner circle until 2003.
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