More than 40 people have been killed in what authorities said was a fierce battle between suspected drug gang gunmen and government forces on a ranch in western Mexico - the deadliest such confrontation in recent memory.
All the dead were suspected criminals except for one federal police officer, who died trying to help a colleague wounded in the shoot-out, national security commissioner Monte Alejandro Rubido said.
Photographs from the scene showed bodies, some with semi-automatic rifles and others without weapons, lying in fields, near farm equipment and on a bloodstained patio strewn with clothes, mattresses and sleeping bags.
Video obtained by The Associated Press showed police coming under fire and bodies strewn throughout a ranch, known as Rancho del Sol.
Mr Rubido said the suspects were members of "a criminal organisation operating in Jalisco state", but did not mention the Jalisco New Generation, the drug cartel that dominates the area where the battle erupted and has grown rapidly in recent years to become one of Mexico's biggest organised crime groups.
The confrontation started in the district of Tanhauto, on the border between Jalisco and Michoacan states, when soldiers, police and state and federal investigators responded to a report of the sudden appearance of armed men on a ranch.
During the operation, federal forces encountered a truck full of armed men who opened fire and when they chased the gunmen on to the ranch, they came under heavy fire by others.
"The rest of the presumed criminals on the property started to attack with intensity," Mr Rubido said.
The federal force called for air and ground support, which included a police helicopter. The size of the 277-acre ranch complicated the battle, which lasted for three hours.
So far authorities have detained three people and confiscated 36 semi-automatic weapons, two smaller arms, a grenade launcher that had been fired and a .50-calibre rifle.
The one-sided casualty list is similar to a controversial case on June 30 last year in which Mexico's army said its troops had engaged in a shoot-out with alleged criminals in which 22 suspects were killed but only one soldier injured. An investigation by The Associated Press revealed that many of suspects had been killed after they surrendered.
Mr Rubido emphasised that both state and national human rights teams were dispatched immediately to investigate the bloodshed at the ranch.
The border of Michoacan and Jalisco states is an area dominated by the Jalisco New Generation cartel and has been the scene of numerous incidents of cartel violence in recent years.
In the nearby town of La Barca, authorities found more than five dozen bodies in mass graves linked to the Jalisco cartel in 2013. Last year gunmen killed the mayor of a nearby town, Tanhuato.
Jalisco New Generation has mounted several large-scale attacks on federal and state forces in recent weeks.
In April, gunmen believed linked to the cartel ambushed a police convoy in Jalisco, killing 15 state officers and wounding five. Earlier this month, New Generation gunmen shot down a military helicopter with a rocket launcher in Jalisco, killing eight aboard.
In just a few years, New Generation has grown from being an offshoot of the powerful Sinaloa cartel to one of Mexico's strongest criminal groups in its own right, according to the US Treasury Department, whose Office of Foreign Assets Control maintains a "black list" of drug trafficking organisations.
New Generation's quick rise reflects a rapidly changing organised-crime landscape in Mexico as the government targets top leaders of established cartels. More than any other criminal group, New Generation has taken advantage of the strategy to hit the leadership of the biggest cartels, strengthening and grabbing territory as its rivals are weakened.