U.S. military drones struck a leftist guerrilla camp inside Venezuela on Friday, according to people in Washington and Venezuela familiar with the operation. The people said the strike killed more than two dozen fighters and was carried out with the cooperation of the Venezuelan government. The camp belonged to the National Liberation Army, known as the ELN, a Colombian guerrilla group that traffics cocaine and gold. It was in Buena Vista del Meta, a hamlet in the remote state of Apure that borders Colombia.

Residents of Buena Vista del Meta reported airborne strikes shortly before dawn Friday against the ELN camp, said Juan Francisco García, an activist for Fundaredes, a group that monitors armed groups and human-rights abuses on the Venezuelan border. “They swept through the area,” García said.

Over two days, 19 bodies had been transferred to the morgue in San Fernando de Apure, the state capital, García said. Another seven bodies remained at the camp. Videos García provided showed remains strewn about the charred site. He said the dead included Colombians and Venezuelans who had been members of the ELN.

Area residents told Fundaredes that over the last month, Venezuelan troops had been deployed to fight the guerrillas, with the drone strikes capping off the operation. “We’ve never had an attack with drones in Venezuela,” García said.

The Venezuelan government did not respond to requests for comment. A spokesman for the Southern Command, which oversees U.S. forces in Latin America, said the command was committed to working with regional partners “to confront and counter narco-terrorist networks,” but could not comment on ongoing operations.

The Trump administration is negotiating an agreement with Venezuela’s interim government that could establish a legal framework for U.S. troops to operate in Venezuela. The status-of-forces agreement, or SOFA, could potentially allow joint military operations, training and other security cooperation. The number of troops and whether U.S. bases would be established would be determined in future negotiations. The report said the administration wants to pacify the country to attract oil investors.

Under former Presidents Hugo Chávez and Nicolás Maduro, the ELN and other armed groups were openly welcomed and used Venezuela as a base from which to launch attacks against the Colombian state. People in Washington and Venezuela familiar with the operation said the interim government led by Maduro’s vice president, Delcy Rodríguez, cooperated with the U.S. operation while the Trump administration applied heavy pressure. Rodríguez has touted a new “agenda of cooperation” with the United States since American forces ousted Maduro in a Jan. 3 operation.

John Polga-Hecimovich, who teaches Latin American politics and military matters at the U.S. Naval Academy, said going after Colombian groups on the border was part of this year’s new phase of cooperation between the United States and Venezuela. “Since the United States took Maduro on Jan. 3, it has been very deliberate, very conscious about trying to reconstruct Venezuela’s security capacity,” he said. “And that involves reclaiming a part of the Venezuelan state from these armed groups.”

The ELN and other Colombian insurgents, including former fighters of the Revolutionary Armed Forces of Colombia, or FARC, who did not participate in a 2016 peace accord, had long found refuge in Venezuela. In 2008, Chávez said FARC had a “political project” that “is welcomed here.”

Interviews with former rebels and guerrilla documents made public by Colombia’s government showed that the ties ran deep, with the Venezuelan government providing arms and supplies. The ELN recruited members inside Venezuela while forming close bonds with the country’s military. Alberto Romero, a former high-ranking Colombian intelligence official, said, “They were brothers in arms.”

The ELN, founded in 1964 by Cuba-inspired revolutionaries, was the first armed group to achieve a robust presence along the entire 1,400-mile border separating Venezuela and Colombia, said Jeremy McDermott, co-director of InSight Crime, a group investigating organized crime in the Western Hemisphere.

The ELN and other armed groups now face a new challenge in Venezuela and Colombia. In Colombia, new conservative President Abelardo de la Espriella has ordered aerial attacks while deploying soldiers on the border. “I’ve ordered a total offensive against the ELN and the dissidents of the FARC,” de la Espriella said last month. “Those miserable narcoterrorists will learn, in the era of the Tiger, how political will turns into concrete action,” said de la Espriella, who calls himself the Tiger.

The report said the United States had also demonstrated it would bomb armed groups and those it said were members of cocaine-trafficking networks. It said U.S. strikes on what it says are drug boats in the Caribbean and Pacific have killed 243 people in 14 months. In Venezuela, the Central Intelligence Agency provided the intelligence that led to a U.S.-Venezuela strike in June that killed the fugitive leader of the Tren de Aragua armed group.

Gerson Arias, an analyst with the policy group Ideas for Peace Foundation in Bogotá, Colombia, said military pressure on both sides of the border was causing communications problems for the ELN. If the offensive continues, he said, it could drive the group deeper into Venezuela. “There’s a strategic impact because the fighters become disconnected from the leaders, from the ELN leadership in Colombia,” he said. Arias and other analysts who track the ELN said a group with so many decades of combat experience would be hard to break.

Luis Eduardo Celis of the Peace and Reconciliation Foundation in Bogotá said the ELN had been battered by military offensives over the years, only to recover. “I think the evidence of the past 62 years shows that the ELN is a force that has grown and shrunk over time, but has managed to survive,” he said. “What happens in Colombia could also happen in Venezuela.”