BOGOTA—Colombia's army killed the military leader of the country's communist guerrillas in a two-day battle that involved airstrikes against his jungle bunker, dealing a major blow to the four-decade insurgency, officials said Thursday.

Victor Suárez, 57 years old, nicknamed "Mono Jojoy," was the second in command and top field marshal of the Revolutionary Armed Forces of Colombia, or FARC, Latin America's biggest and oldest guerrilla group. To many ordinary Colombians, his thick moustache and Che Guevara-style black beret were synonymous with the FARC.

"Mono Jojoy is dead," Colombian President Juan Manuel Santos told reporters in New York, where he is attending the United Nations General Assembly. "This is the most devastating blow ever dealt to the FARC."

The strike was a big boost for Mr. Santos, who took office in August. He dubbed the military mission, which involved more than 30 aircraft, "Operation Welcome." In his role as defense minister under Colombia's previous president, Álvaro Uribe, Mr. Santos oversaw some notable blows against the FARC.

The death of Mr. Suárez, also known by his nom de guerre Jorge Briceño, could cripple the FARC's so-called eastern block, its most powerful fighting force based in the country's southeastern plains. Analysts said it could nudge the guerrillas, who number between 6,000 and 7,000 fighters, toward seeking peace.

Mr. Suárez, who reputedly joined the guerrillas at age 12, had a reputation for brutality. He was linked to a 2003 car bombing in Bogota that left scores dead and to the 2002 kidnapping of Ingrid Betancourt, a former presidential candidate who was freed in a military operation two years ago. The U.S. offered a $5 million reward for his capture.

His death is the latest in a string of devastating blows to the FARC, which once threatened to overrun the country and has increasingly turned to drug trafficking to fund its activities.

In 2008, Raul Reyes, then second-in-command of the FARC, was killed in a controversial crossborder raid in Ecuador that caused Quito to protest its sovereignty had been violated. Shortly after, the FARC's founder, Manuel Marulanda, known as "Tirofijo" or "Sure Shot," died from an apparent heart attack.

U.S. officials praised the operation against the FARC, considered a terrorist group by Washington and Europe.

"This is an important victory for Colombia," said National Security Council spokesman Mike Hammer. President Barack Obama is scheduled to meet with Mr. Santos on Friday in New York to discuss this and other developments, said Mr. Hammer.

Soldiers identified Mr. Suárez's body after two days of combat earlier this week against what Colombian officials described as the rebels' military nerve center. Mr. Suárez's headquarters had a concrete bunker complete with escape tunnels, Defense Minister Rodrigo Rivera told a news conference.

About 20 guerrillas who guarded Mr. Suárez were killed, Mr. Santos said. Five soldiers were wounded. Mr. Rivera said the only government fatality was a bomb-sniffing dog named Sasha.

The operation was helped by undercover intelligence gathered from close associates of Mr. Suárez. Such intelligence operations are becoming a hallmark of Colombia's armed forces, which have received billions of dollars in U.S. aid. In 2008, Colombian forces released Ms. Betancourt and other hostages by posing as members of nongovernmental peace groups.

Mr. Rivera, the defense minister, renewed a call to FARC leaders to turn themselves in. "Surrender and we will guarantee your lives," he said.

The FARC has been fighting successive Colombian governments since 1964. In the late 1990s, the FARC numbered around 18,000 fighters and threatened to encircle Bogota. Former President Uribe made the fight against the guerrillas his central aim, and put them on the run.

After Mr. Santos took power, the FARC's top commander, Alfonso Cano, issued a communiqué asking for international mediators to negotiate peace. But at the same time, the guerrillas embarked on a military offensive ambushing soldiers and police in remote coca-growing areas of Colombia, and allegedly planting a bomb in Bogota.

Mr. Santos was beginning to feel political heat, as Colombians wondered whether he would be able to maintain the gains made by Mr. Uribe. On Thursday, Mr. Santos vowed to continue the campaign against the guerrillas. "This was Operation Welcome," he said in New York. "To the rest of the FARC—We are going after you."

Mr. Suárez's death is likely to further demoralize the FARC, whose ranks in recent years have been decimated by desertions.

"This will leave a huge gap in the top levels of the guerrilla leadership…and may well force Cano to consider seriously the negotiation option," said Bruce Bagley, a Colombia expert at the University of Miami.

The group could stage attacks in the coming weeks, however.

"They will try to show that they are viable, but it won't be major," said Jay Cope, senior research fellow at the U.S.'s Institute for National Strategic Studies in Washington.

Colombian officials said they were also on the trail of Mr. Cano, the leader of the FARC's seven-man secretariat.

Unlike Mr. Cano, a bearded and bespectacled former communist student leader, Mr. Suárez came from a peasant background and rose through the ranks. It is believed his mother was also a guerrilla, and a cook for Jacobo Arenas, one of the FARC's founders. Through Mr. Suárez's career, he developed a reputation for imparting harsh discipline to guerrillas who broke regulations.

"He was the epitome of the drug-fueled fighting FARC," said a Colombian official.

At the time of his death, Mr. Suárez had been indicted on drug charges in the U.S. and had warrants outstanding and convictions in absentia in Colombia for crimes including murder, kidnapping, drug trafficking and terrorism.

A businessman as well as a fighter, Mr. Suárez is believed by analysts to have amassed a herd of 30,000 cattle in Caqueta state, in southeastern Colombia.