MEDELLÍN, Colombia — Colombia’s fragile peace was shaken on Wednesday as the National Liberation Army, a guerrilla group known as the ELN, attacked a military base and an oil pipeline just hours after a 102-day cease-fire ended, the government said.
While no deaths were reported, the attacks underscored the steep challenges Colombia faces as it tries to negotiate a peace deal with the ELN similar to the one that it signed with the Revolutionary Armed Forces of Colombia, or FARC, in 2016.
The attacks by the ELN also came days ahead of an expected visit to Colombia by the United Nations secretary general, António Guterres, to monitor the peace process.
President Juan Manuel Santos said in a statement that “the national government was always open to extending the cease-fire with this group and negotiating a new one.” But he added, “Inexplicably, the ELN didn’t just refuse but resumed attacks this morning.”
He said he had recalled the leader of his team involved in peace negotiations with the rebels.
Mr. Santos won a Nobel Peace Prize in 2016 for his role in the deal with the FARC. But security analysts say that the ELN is far less organized and more ideological, and that Mr. Santos, whose term ends this year, has few viable paths to sign a peace agreement with a group that seems interested in continuing attacks.
“The ELN is disconnected from the electoral reality,” said Jairo Libreros, a professor at the Externado University in Colombia who follows the group. Mr. Libreros said that the rebel group appeared to think that acts of violence would make Colombians “rise up to call that the government signs a peace deal.”
The attacks appeared to be typical for guerrillas: a midnight raid on a military base in the eastern department of Arauca, in which commandos threw a grenade at soldiers guarding a post, injuring several them. Near the town of Aguazul, about 100 miles from Bogotá, the capital, another group bombed an oil pipeline, the government said.
The guerrillas defended their decision to resume attacks. The main purpose of the cease-fire, “to improve the humanitarian situation of the population, was hardly achieved by the regime,” it said in a statement. “We delivered on the objectives.”
The guerrillas said the attacks on Wednesday had “occurred in the middle of a complex situation of conflict in the country.” It called on the government to resume talks but did not offer another cease-fire.
Few in Colombia believed the recent cease-fire would last. Announced in late August ahead of a visit by Pope Francis, it was seen as a temporary concession by both sides to the pontiff who had come to promote an end to the country’s multiple conflicts.
Mr. Libreros said the agreement had been violated at least twice; late last year, a massacre by the guerrillas killed more than a dozen people, including an indigenous leader.
The ELN, founded in 1964, has seen its presence dwindle in Colombia in recent years amid desertions and government-led attacks. Some analysts estimate that their force is now as small as 1,000 fighters.
With the FARC peace deal, however, the ELN became the largest remaining rebel group in Colombia and tried to take on the mantle as leader of Marxist struggle in the country.
Its insistence to keep fighting reduces hope that a peace agreement is on the horizon even if talks resume, said Camilo González Posso, the director of the Institute for Development and Peace Studies, a Bogotá-based group.
“In the government there are sectors that think it’s a waste because it won’t result in anything,” Mr. González said. “And in the ELN they believe the government won’t follow through and that it’s losing ground with cease-fires.”