The leader of Colombia's left wing Farc rebel group, Alfonso Cano, has been killed in a military raid, President Juan Manuel Santos has confirmed.
He called it the most devastating blow to the group in its decades-long insurgency and urged it to disband.
Defence Minister Juan Carlos Pinzon said Cano was killed in an operation in mountains in Colombia's south-west.
Security forces have killed a number of Farc commanders and arrested many others in recent years.
Giving details of the operation, Mr Pinzon said government forces first bombed a Farc jungle camp in Cauca state.
Troops were then lowered from helicopters to search the area and killed Cano and several other Farc (Revolutionary Armed Forces of Colombia) members in a gun battle.
'Prison or a tomb'
Pictures of the dead leader, with his trademark bushy beard shaved off, were broadcast on Colombian television.
"It is the most devastating blow that this group has suffered in its history," President Santos said in a televised address.
"I want to send a message to each and every member of that organization: demobilise... or otherwise you will end up in a prison or in a tomb. We will achieve peace."
Cano, 63, was reportedly tracked down to the jungle camp with the aid of telephone intercepts.
Colombia had offered a reward of nearly $4m (£2.5m) for information leading to his capture.
Analysts say Cano's death deals a further blow to the rebel group's ability to co-ordinate attacks on security forces and other targets.
The Marxist-inspired Farc has already been weakened by a military offensive which began 10 years ago.
Mr Cano, a former academic from Bogota, became the Farc's leader in 2008 after his predecessor, Manuel Marulanda died of a heart attack.
His real name was Guillermo Leon Saenz.
In July, he narrowly escaped a raid on his camp, Colombian officials said.
In September 2010, Mono Jojoy, another top Farc commander, was killed in a bombing raid.
The Colombian army also said earlier this year that it had killed Mr Cano's head of security, Alirio Rojas Bocanegra.
The military has been able to expand its operations against the rebels with the help of the US, which has provided billions of dollars in funding, training and intelligence-sharing.
However, the Farc - the oldest and largest among Colombia's left-wing rebel groups - retains the ability to mount hit-and-run attacks, partly owing to cash raised through its involvement in the illegal drugs trade and partly thanks to the country's thick jungles.
The Farc is on US and European lists of terrorist organisations.
Colombia's civil conflict has lasted more than four decades, drawing in left-wing rebels and right-wing paramilitaries.