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An arson attack on a casino in the northern Mexican city of Monterrey has killed more than 50 people.
Several gunmen burst into the building in broad daylight, dousing it with fuel and setting it alight.
Amid the panic, many people were trapped and overcome by smoke.
Officials suspect organised crime was behind the attack, one of the deadliest since President Felipe Calderon launched his crackdown on the cartels in December 2006.
In a tweet, Mr Calderon said the attack was "an abhorrent act of terror and barbarism" that requires "all of us to persevere in the fight against these unscrupulous criminal bands".
The attack happened mid-afternoon when about 100 staff and customers were inside the Casino Royale.
Officials initially said 53 people had died but on Friday the state governor, Rodrigo Medina, lowered this to 52.
One survivor said the gunmen burst in, threatened them and then sprayed some kind of fuel which they set alight.
"It was chaos inside. You couldn't see and the smoke was choking us. Some people didn't reach the exit and fell just metres from the door," said one woman who got out.
Another person who managed to escape said there was complete panic.
"We all wanted to get out at the same time, there was a lot of pushing and we fell to the floor," another woman told Mexican media.
"I just heard explosions and ran to save my life".
Officials said some people had hidden in toilets and offices when they heard explosions instead of trying to get out and had suffocated as smoke engulfed the building.
Some reports suggested the emergency exits had been locked.
TV images showed relatives outside the casino demanding information about their loved ones.
"My wife came here for a celebration... she was having dinner with her friends," one man told Milenio TV.
State Attorney General Leon Adrian de la Garza said a drug cartel was believed to be behind the attack.
Officials suggested the fire may have been in reprisal for failing to pay extortion money, the Excelsior newspaper reported.
Home to some of Mexico's largest companies, Monterrey and the state of Nuevo Leon have seen rising violence as the Zetas and Gulf cartels vie for control of trafficking routes to the US.
The drug gangs are also increasingly involved in kidnapping and extortion.
Analysis
Julian Miglierini
BBC News, Mexico City
--------------------------------------------------------------------------------
Even by the gruesome standards of violence in the areas of Mexico most affected by drug-related violence, Thursday's attack has no precedent. It took place in broad daylight, at the heart of Mexico's third-largest city, and was aimed at innocent civilians.
Why did it happen, Mexicans are asking themselves. Is it a revenge attack, part of a feud between rival drug gangs? A punishment for refusing to pay an extortion fee? A way to instil fear in the people of Monterrey, a city that has descended into a spiral of violence? The answers are not clear yet.
President Felipe Calderon branded it an "act of terror", strong language that has not been used often by the government to describe Mexico's long-running drug conflict.
But for the people of Monterrey, a city that only a few years ago used to enjoy a reputation as one of the safest in Latin America, "terror" is a word that has become all too common recently - even more so after Thursday's attack.
BBC News - Mexico casino arson attack kills dozens in Monterrey
Several gunmen burst into the building in broad daylight, dousing it with fuel and setting it alight.
Amid the panic, many people were trapped and overcome by smoke.
Officials suspect organised crime was behind the attack, one of the deadliest since President Felipe Calderon launched his crackdown on the cartels in December 2006.
In a tweet, Mr Calderon said the attack was "an abhorrent act of terror and barbarism" that requires "all of us to persevere in the fight against these unscrupulous criminal bands".
The attack happened mid-afternoon when about 100 staff and customers were inside the Casino Royale.
Officials initially said 53 people had died but on Friday the state governor, Rodrigo Medina, lowered this to 52.
One survivor said the gunmen burst in, threatened them and then sprayed some kind of fuel which they set alight.
"It was chaos inside. You couldn't see and the smoke was choking us. Some people didn't reach the exit and fell just metres from the door," said one woman who got out.
Another person who managed to escape said there was complete panic.
"We all wanted to get out at the same time, there was a lot of pushing and we fell to the floor," another woman told Mexican media.
"I just heard explosions and ran to save my life".
Officials said some people had hidden in toilets and offices when they heard explosions instead of trying to get out and had suffocated as smoke engulfed the building.
Some reports suggested the emergency exits had been locked.
TV images showed relatives outside the casino demanding information about their loved ones.
"My wife came here for a celebration... she was having dinner with her friends," one man told Milenio TV.
State Attorney General Leon Adrian de la Garza said a drug cartel was believed to be behind the attack.
Officials suggested the fire may have been in reprisal for failing to pay extortion money, the Excelsior newspaper reported.
Home to some of Mexico's largest companies, Monterrey and the state of Nuevo Leon have seen rising violence as the Zetas and Gulf cartels vie for control of trafficking routes to the US.
The drug gangs are also increasingly involved in kidnapping and extortion.
Analysis
Julian Miglierini
BBC News, Mexico City
--------------------------------------------------------------------------------
Even by the gruesome standards of violence in the areas of Mexico most affected by drug-related violence, Thursday's attack has no precedent. It took place in broad daylight, at the heart of Mexico's third-largest city, and was aimed at innocent civilians.
Why did it happen, Mexicans are asking themselves. Is it a revenge attack, part of a feud between rival drug gangs? A punishment for refusing to pay an extortion fee? A way to instil fear in the people of Monterrey, a city that has descended into a spiral of violence? The answers are not clear yet.
President Felipe Calderon branded it an "act of terror", strong language that has not been used often by the government to describe Mexico's long-running drug conflict.
But for the people of Monterrey, a city that only a few years ago used to enjoy a reputation as one of the safest in Latin America, "terror" is a word that has become all too common recently - even more so after Thursday's attack.
BBC News - Mexico casino arson attack kills dozens in Monterrey