Colombia's army says it has killed the security chief for the head of the country's main rebel group, the Revolutionary Armed Forces of Colombia.

An army spokesman said Saturday that Alirio Rojas Bocanegra, known as “El Abuelo,” or “The Grandfather,” had been killed.

He was reported to have died in an operation in Tolima, an area more than 200 kilometers southwest of the Colombian capital, Bogota.

The army said Rojas was the leader of security forces for the FARC's top commander, who goes by the alias “Alfonso Cano.”

In an apparent reference to the operation that killed Rojas, Colombian President Juan Manuel Santos posted a message on Twitter announcing “a new great blow to the FARC.”

Rojas reportedly served for at least 23 years in the leftist guerrilla group which has been designated as a terrorist organization by Colombia, the United States and the European Union.

FARC rebels have been at war with the Colombian government since the 1960s.

While most of the group's funding comes from cocaine trafficking and extortion, the leftist rebels are believed to be holding an unknown number of people for ransom or political leverage.

Earlier this week, President Santos announced that a top FARC commander had been captured across the border in Venezuela in a joint effort by the two countries.

Ties between Colombia and Venezuela have been strained over Colombia's accusations that Venezuela harbors top FARC officials.