One of Mexico’s most notorious drug lords, Nemesio Oseguera, or “El Mencho,” was killed in a military raid on Sunday, sparking widespread retaliatory violence.

President Claudia Sheinbaum has been under mounting pressure from Washington to intensify her offensive against drug cartels blamed for producing and smuggling drugs, particularly the synthetic opioid fentanyl, across the border to the US.

Oseguera, 60, the mastermind of the powerful Jalisco New Generation Cartel (CJNG), died in custody after being injured in a military operation by Mexican special forces in the town of Tapalpa on Mexico’s Pacific coast in Jalisco state, according to Mexico’s defence ministry.

His corpse arrived in Mexico City on Sunday afternoon in a heavily guarded convoy of National Guard troops.

Mexican forces led and carried out the raid with intelligence support from the US, sources said. A new US-military-led task force played a role, a US defence official told Reuters. Mexico’s defence ministry said it received “complementary information” from the US.

After reports of El Mencho’s death, cartel henchmen blockaded highways with burning cars and torched businesses in more than a half a dozen states, paralysing parts of the country. No civilian deaths have been reported.

In Jalisco’s popular beach resort of Puerto Vallarta, frightened tourists on social media described a “war zone” as plumes of dark smoke rose into the sky from around the bay. Air Canada, United Airlines , Aeromexico and American Airlines suspended flights in the area.

Former cop to cartel kingpin

Oseguera, a former police officer, founded and oversaw the rapid rise of the CJNG, named for the western state of Jalisco that is home to one of Mexico’s biggest cities, Guadalajara.

In recent years, CJNG has expanded into one of Mexico’s most powerful cartels, known for violent tactics including forced labor and forced recruitment.

Under El Mencho’s leadership, CJNG also became a highly diversified criminal enterprise, expanding from drug trafficking to fuel theft, extortion, human smuggling, and complex financial frauds. The cartel pioneered use of drones in attacks against civilians in remote regions of western Mexico as part of its rapid territorial expansion.

Sunday’s raid was one of Mexico’s highest profile blows against drug gangs responsible for smuggling billions of dollars of drugs - including fentanyl - into the US In recent years, the leaders of the rival Sinaloa Cartel - Joaquin ‘El Chapo’ Guzman and Ismael “El Mayo” Zambada- were captured alive. Both are now in US prisons.

President Donald Trump’s administration lauded El Mencho’s killing, but domestic violence it triggered highlighted the political balancing act Sheinbaum must strike as her government escalates its cartel offensive.

On Sunday, Sheinbaum stressed that activities in most areas of the country were proceeding as usual. Schools in various states across Mexico protectively canceled classes for Monday, according to announcements by state-level education departments.

Security experts were watching whether the raid and death of the cartel boss will fracture CJNG leadership and trigger bloody infighting.

“There will definitely be skirmishes between the various factions, and these spasms of violence could last for years,” said Carlos Olivo, a former US Drug Enforcement Administration assistant special agent in charge and an expert in CJNG.

Killing wins US praise

US Deputy Secretary of State Christopher Landau, previously ambassador to Mexico, said Oseguera’s killing was a “great development” for the US and Mexico, as well as the rest of Latin America.

In January after the US capture of Venezuelan President Nicolas Maduro, Trump said “the cartels are running Mexico,” and warned “we are going to start now hitting land with regard to the cartels.”

Sheinbaum said she would strengthen efforts to cooperate with the US to fight cartels., but vowed to uphold Mexico’s sovereignty and warned against any unilateral military action by the US in Mexico.

Sheinbaum in a social media post on Sunday said security officials would provide information on the operation.