Mexican authorities has offered a reward worth over €1.6m for information leading to the arrest of armed men who torched a casino, killing at least 53 people.
Analysts and officials said the assault had all the hallmarks of drug cartels that have plunged Monterrey and other parts of Mexico into a spiral of violence.
The latest attack is one of the worst in a major Mexican city in years.
A survivor said the armed men burst into the Casino Royale in the prosperous industrial city of Monterrey yesterday afternoon and threatened gamblers before spraying petrol on the carpets and setting it on fire.
The particularly callous attack shocked a nation already used to grim murders and high tolls in a drug war that has claimed more than 41,000 lives since a military crackdown began in 2006.
One witness said people stampeded after hearing blasts soon after the attack began.
Many patrons ran to hide in the toilets but died from asphyxiation as smoke engulfed the building, a rescue official said.
Rodrigo Medina, governor of Nuevo Leon state, told the Televisa network that 53 people were killed and rescue teams warned the death toll could rise.
Media reports said the majority of those killed were women.
Monterrey, 230km from the Texas border, is a relatively wealthy city of about 4 million people and was for years seen as a model of economic development.
But lawlessness has taken its toll as Mexico's drug war has escalated.
President Felipe Calderon called the attack a ‘barbaric act of terror’ and vowed to keep fighting organised crime.
Rival drug gangs are fighting for control of Monterrey and routinely extort casinos and other businesses, threatening attacks if the owners refuse to pay.
Televisa said up to 20 more bodies still might be trapped in the debris of the casino. Paramedics and firefighters pulled out bodies covered with plastic bags from a hole in the wall as night fell.
Twitter users in Monterrey reported scenes of chaos on the streets around the Casino Royale after the attack and heavy army presence.