Former general Mario Montoya is one of hundreds of military personnel under investigation for the extrajudicial killing of at least 6,400 people falsely identified as enemy fighters.

The practice, known in military circles as "false positives," was aimed at inflating the army's successes in fighting the Revolutionary Armed Forces of Colombia (FARC), some soldiers and officials have told the court.

Montoya, 74, is accused of pressuring the men under his command "to obtain combat casualties" at any cost, between 2002 and 2003, Catalina Diaz, a magistrate with the Special Jurisdiction of Peace (JEP) court, told journalists.

The JEP was set up after the signing of a 2016 peace deal between the government and the once-powerful FARC insurgent group, to try the worst crimes committed during the half-century conflict.

Diaz said Montoya is accused of "lying about the number of casualties" to inflate the kill rate when he headed an army brigade, and of "using violent language" that "praised bloodshed."

Montoya was army chief from 2006 until he resigned in 2008 under fire over the extrajudicial killings he said took place behind his back.

In 2021, he was also charged over 104 similar killings committed between 2007 and 2008, in a case which remains under investigation.

Diaz said "combat deaths" were seen as the "only indicator of success to receive incentives, awards, or not to be transferred or retired from the army."

The JEP has charged Montoya and eight other soldiers with war crimes and crimes against humanity.

They have 30 days to admit or deny the facts.

Under the peace deal, the court can offer alternatives to jail time or lesser sentences to people who confess their crimes and make reparations to victims.

If they do not confess, and are found guilty, they could face a stiffer jail term.

The tribunal has yet to hand down any sentences since it began operations in 2018.