The Colombian government says another senior commander of the Farc rebel group has been killed.
Rios was the youngest member of the Farc's seven-man secretariat
Defence Minister Juan Manuel Santos said Ivan Rios had been killed by his own men. Earlier the army had claimed he had died in combat with its troops.
The reported death comes less than a week after another top commander Farc leader, Raul Reyes, was killed by troops in a raid just inside Ecuador.
That killing sparked a diplomatic row, with Ecuador denouncing the incursion.
Ivan Rios - whose real name was Manuel Munoz Ortiz - was the youngest member of the seven-man secretariat of the Revolutionary Armed Forces of Colombia, or Farc.
He is said to have been killed in a mountainous area of the western province of Caldas.
Mr Santos said the Farc's chief of security gave Colombian troops the leader's severed hand as proof of his death. It is unclear why he was killed.
The death came as Latin American leaders exchanged accusations at a regional summit over Saturday's cross-border raid.
Ecuadorean President Rafael Correa condemned Colombian "aggression" in his opening speech in the Dominican Republic.
His Colombian counterpart, Alvaro Uribe, responded with claims that Mr Correa had links to Farc rebels and had not co-operated in fighting terrorism.
Mr Uribe, who is backed by Washington, has made the military defeat of the Farc a priority.
This loss of senior commanders are the latest in a series of blows for the rebels.
But the BBC's Jeremy McDermott in Colombia says there is a growing call, both internationally and domestically, for negotiations as the only sure way to end the four-decade conflict.