Six Mexican soldiers were killed in a rocket-propelled grenade attack on an army helicopter Friday, in one of the highest single military death tolls so far in the country's US-backed drug war.

Mexico's national security commissioner updated the toll of soldiers killed in the attack from three to five on Monday morning. By afternoon, Monte Alejandro Rubido said six soldiers were dead.

In all, 15 people were killed, he said in an afternoon radio interview, more than doubling the previous death toll of seven overall.

Commissioner Rubido said DNA tests were conducted on remains found after the helicopter came under attack and was forced to make an emergency landing at 7 am on May 1.

The Canadian-made Cougar helicopter carried 18 passengers and was traveling with other choppers over a remote highway connecting the towns of Casimiro Castillo and Villa Purificación, in the western state of Jalisco. They came upon an armed convoy of vehicles, which opened fire on the helicopters.

Initially, authorities said three passengers were considered missing after the RPG fire, which hit one chopper's tail rotor. The incident fueled speculation of an attempted capture of the leader of the increasingly powerful Jalisco New Generation cartel.

That morning, Mexico's government had officially launched a joint-agency "Operation Jalisco," aimed at dismantling the cartel, known by its Spanish initials CJNG. The cartel has carried out some of the most brazen attacks on Mexican security forces in recent years.

Cartel operatives set 39 vehicles on fire across four states. (Photo by Victor Hugo Ornelas/VICE News)

It was the start of a chaotic day across Jalisco and three other states in western Mexico.

Suspected cartel operatives placed 39 narco-blockades from Colima to Nayarit, with coordinated blockades affecting Mexico's second largest city, Guadalajara, and the tourist resort of Puerto Vallarta.

Gas stations and banks were set on fire and at least 19 people were arrested, Rubido said Monday. Local news media outlets described it as the worst outbreak of narco-blockades in Jalisco since the emergence in 2010 of the New Generation cartel.

By day's end, at least seven people were reported killed. On Monday afternoon, the government said that toll was now 15 — eight suspected cartel members, one state judicial police agent, and the six soldiers.

'We can't let these terrorists intimidate the state.'

Jalisco's attorney general called Friday's cartel assault "pure terrorism" in a radio interview on Monday. "We can't let these terrorists intimidate the state," said Jalisco prosecutor Luis Carlos Nájera.

None of the cartel's top leaders were detained, Rubido said. The New Generation cartel chief, Nemesio Oceguera Cervantes, a reclusive figure known as "El Mencho," remains at large.

Servando Gomez, the leader of the Knights Templar cartel, was captured in late February. (Photo via AP)

Friday's violence in Jalisco left one of the highest death tolls ever for Mexico's military since the start of the drug war in late 2006. In a non-combat accident blamed on weather, 11 soldiers died after a military helicopter crashed in the state of Durango in June 2010.

Alejandro Hope, a security analyst in Mexico City, said it was likely Mexico's army was close to capturing the CJNG leader on May 1, which would explain the virulent reaction of the group against so much territory in Mexico's west. The attacks also demonstrated that the New Generation cartel's infrastructure is intact and organized, he added.

"When they captured El Chapo, there was no reaction from anybody," Hope told VICE News. "This is going to be personal now for the military."

The government's operation against the CJNG would be escalating, Rubido said.

"There will be significant use of force by the Mexican state against these criminals," the commissioner said in a televised phone interview on Canal 2. "We can't rule out similar incidents in the eventuality of taking action against the leader of the criminal organization."

News anchor Carlos Loret de Mola asked Rubido if the government was winning the war against the cartels, to which the national security commissioner responded by saying that the strategy of capturing top cartel leaders across the country was proving successful.

Since February 2014, the administration of President Enrique Peña Nieto has captured Sinaloa cartel leader Joaquin "El Chapo" Guzmán, considered one of the most powerful narco chiefs in Mexican history, as well as Knights Templar leader Servando Gómez Martínez, aka "La Tuta," among others.

"I wouldn't speak of a war," Rubido said. "We've hit, without exception, the principal heads of all the criminal groups."