By TYLER BRIDGES

The death of the longtime leader of Colombia's largest and most powerful guerrilla group plunges the insurgency -- already on the run from a government offensive -- into an uncertain future.

Manuel ''Sure Shot'' Marulanda died March 26 of natural causes, guerrilla senior commander Timoleón Jiménez confirmed Sunday in a video broadcast by the Venezuela-based Telesur network. He was 78 or 80 years old.

Jiménez corroborated a statement made Saturday by the Colombian Ministry of Defense that many found hard to believe because Marulanda's death has been frequently reported over the years.

Marulanda died ''in the arms of his companion, surrounded by bodyguards and all the units that comprised his security,'' Jiménez said, adding that Marulanda's death came after an undisclosed illness.

Jiménez also confirmed the Ministry of Defense's report that guerrilla leader Alfonso Cano would succeed Marulanda.

Marulanda's death ends an era that began in 1964 with the founding of the Revolutionary Armed Forces of Colombia, Latin America's oldest insurgency. As other guerrilla groups came and went throughout Latin America -- many of them supported in the 1960s by Fidel Castro -- the FARC survived, taking advantage of rural poverty to find recruits and using Colombia's jungles and mountains to operate relatively freely until recent years.

Marulanda's death marks another major victory in an all-out effort that President Alvaro Uribe has waged against the FARC since 2002.

Uribe's government wasted no time in trying to capitalize on Marulanda's passing. Uribe called on guerrillas holding 700 kidnap victims to desert and free the hostages, including former presidential candidate Ingrid Betancourt.

Those who did so, Uribe added, could qualify for financial rewards and resettlement outside Colombia.

A WARNING

Defense Minister Juan Manuel Santos called on Cano and another FARC leader known as Mono Joyjoy to negotiate a peace deal with the government, or else.

''We already have three of the seven members of the FARC ruling secretariat below ground, and to the others, we say that they are running the same risk, that they open their eyes and take this advantage and enter the door of peace,'' Santos said in a statement.

In March, Colombian commandos killed the FARC's second-in-command, Raúl Reyes, and less than a week later, a FARC soldier killed Iván Ríos, another member of the ruling secretariat, and claimed the bounty on Ríos' head.

Karina, the FARC's senior female commander, surrendered a week ago and called on other FARC soldiers to turn themselves in. She said she saw no future for the guerrilla insurgency.

Senior Colombian intelligence officials told The Miami Herald in March that the FARC had about 10,000 troops, down from 16,900 in 2002, as a government offensive -- funded in part by the United States -- has steadily produced deaths, desertions and captures.

Adam Isacson, a Colombia expert with the Center for International Policy in Washington, said Marulanda's death likely will lead to a debilitating power struggle over his succession. Or, he said, the FARC could simply disintegrate.

But Isacson also did not discount Marulanda's death strengthening the FARC as new blood takes over.

'If Marulanda's chosen successor, Alfonso Cano, is actually able to command the remaining top FARC leaders -- a big `if' -- the FARC could become more dangerous,'' Isacson said in an e-mail. ``If the group's decision-making process becomes less hidebound and sluggish, it may pose more of a threat on the battlefield.''

He added: 'It will also be interesting to see whether Cano, who is thought to lead the more moderate, `political' faction of the FARC, takes steps to improve the guerrillas' image among poor Colombians. For years, the FARC has appeared to believe that drug money and military capabilities could somehow substitute for hearts and minds.''

Shelley McConnell, a Colombia expert at Hamilton College, said she doesn't foresee the FARC's rapid demise. ''The FARC is a business, and Colombia's war is driven by things other than ideology,'' McConnell said in an e-mail. ``The structures that drive the violence are far broader than one man, and include things like the U.S. demand for cocaine and the ongoing poverty in Colombia, which will not change with one man's death.''

In a speech Sunday in Uruguay, Nicaraguan President Daniel Ortega praised Marulanda, extending his ''solidarity'' and ''condolences'' on the loss of ``an extraordinary fighter.''

Marulanda was born Pedro Antonio Marín to a peasant family and left school during the fifth or sixth grade. He took up arms in 1949 as Colombia descended into years of bloodshed known as "La Violencia.''

CREATION OF FARC

Marulanda became a communist when he helped create the FARC to battle the government. But authors and journalists given the rare opportunity to interview him over the years said that while Marulanda saw himself as fighting to overthrow Colombia's corrupt political system and give the poor a greater share of wealth, he rarely discussed Marxist theory. He acquired his nickname for his dead aim with a rifle.

''In many ways, Marulanda personified the contemporary history of Colombia,'' said Marc Chernick, a Georgetown University professor who recently authored a book in Spanish on the country's violence. ``He lived through all the phases of violence, from the partisan civil war in the 1940s and 1950s to the Marxist guerrilla insurgency of the 1960s and 1970s to the drug-fueled post-Cold War violence. He represents all the multiple conflicts that have endured in Colombia all these years.''

Miami Herald special correspondent Benjamin N. Gedan contributed to this report from Uruguay.