Colombian troops killed Alfonso Cano, leader of the FARC (Revolutionary Armed Forces of Colombia), during a day-long operation in which his female companion also died, government and local officials said.

Cano died in a firefight late Friday during a massive anti-guerrilla effort involving 800 to 1,000 soldiers as part of Bogota's latest push against the leftist rebels.

President Juan Manuel Santos hailed Cano's demise as "the strongest blow sustained by the guerrilla group in all of its history," and he warned the FARC to lay down their arms.

"Demobilize or you will end up in prison or in a grave," the president said.

Cano's body has been taken to a morgue in the city of the Popayan for an autopsy to determine the official cause of death, authorities said Saturday.

The operation was the latest in a string of recent military victories in the government's quest to eradicate Latin America's longest-running leftist insurgency, after years of unsuccessful attempts to find a negotiated solution.

Defense Minister Juan Carlos Pinzon said Cano was killed in a military operation launched in southern Cauca department several days ago. The rebel leader's female companion also died during the battle, military officials said.

According to Pinzon, the military early Friday started to hit an area occupied by FARC rebels, followed by a ground offensive to encircle the area, cutting off escape routes.

A firefight erupted when the soldiers caught up with 63-year-old Cano and his personal security detail, and the FARC leader was killed in action, Pinzon said.

The military had been hunting the FARC leader for months, initially believing that he was hiding in Tolima, Valle or Huila departments, officials said.

But he was initially able the evade his trackers, moving south apparently in the hope of securing protection from guerrilla fronts operating in Cauca. But faced with fierce government bombardments, they were unable to help him.

"This is a key moment for the FARC," stressed former Colombian president Andres Pastrana.

"Those in its leadership who still remain alive should think very seriously about starting peace negotiations in order to end this war for the benefit of all Colombians."

Cano, whose real name was Guillermo Leon Saenz Vargas, assumed control of the FARC in March 2008, when its reclusive founder and revered leader, Manuel "Sure Shot" Marulanda Velez, who was last seen in 1982, died after a brief illness.

The FARC is Colombia's oldest and largest guerrilla force, believed to have 8,000 members, and has been at war with the government since its launch in 1964.

It began a campaign of kidnappings in the mid-1980s, seizing army hostages to serve as bargaining chips for FARC prisoners. By the late 1990s civilians and political leaders were also being snatched, winning the group greater notoriety and increased influence with its government interlocutors.

Alfredo Rangel, a political expert from the Foundation for Security and Democracy, in Bogota, said Cano's death was extremely significant.

"This was the most painful loss for the FARC since the deaths of Reyes and 'Sure Shot' Marulanda," he said. "It will be very difficult for the insurgents to replace him."

Cano hailed from a middle class family: his father was an agronomist, his mother a teacher.

He studied law and anthropology at the National University in Bogota, where he is remembered as an avid scholar of history and other social sciences.

He earned his stripes in the Communist Party and joined the FARC in the 1970s where he quickly rose through the ranks becoming the group's chief ideologist.

Throughout his career as a guerrilla leader, Cano combined military strikes with attempts to consolidate gains made by the insurgents through negotiations with the government.

Shortly before the 2010 inauguration of President Santos, Cano made public a video in which he called for a peaceful resolution of the conflict in Colombia.

But there was no evidence of recent contacts between the FARC and the government.