Government forces in Colombia have killed a FARC brigade commander close to the group's chief negotiator, the country's defence minister said.

Juan Carlos Pinzon, the defence minister, said that Jacobo Arango, a FARC commander in a northwestern area straddling Cordoba and Antioquia provinces, a known drug route, was among six rebels killed in an assault on Thursday.

"It's a strike of great importance," he told reporters on Friday.

Arango was close to chief FARC peace negotiator Ivan Marquez, who was also Arango's direct commander, and he had been a rebel for more than three decades, Pinzon said.