Monterrey, Mexico (CNN) -- Hundreds of troops headed to northern Mexico Saturday as authorities continued investigations into the torching of a casino that left at least 52 people dead.
Mexico's president, who described the attack as an act of terrorism, ordered the deployment of 1,500 troops to the city of Monterrey over the next three days, the country's defense department said in a statement.
State officials released composite sketches of three suspects. And Mexico's Attorney General's Office said it was offering a 30-million peso ($2.4 million) reward for information leading to the capture of men they suspect were behind Thursday afternoon's attack in the affluent city.
The ambush left a charred shell where a high-end casino once stood. Photos of the scene at the Casino Royale showed singed slot machines. A video released by Mexican authorities showed armed men bursting into the casino carrying what appeared to be gallons of gasoline. Seconds later, dozens of people fled as smoke and fire engulfed the building.
On Saturday, 300 soldiers from the Mexican Army and Air Force boarded planes in the nation's capital, bound for Monterrey as part of Calderon's plan to help local authorities fight drug trafficking and organized crime, Mexico's defense department said.
Investigators were still trying to identify seven of the 52 people killed in Thursday's attack, Mexico's state-run Notimex news agency reported Saturday.
The staggering number of victims drew national attention in a country where headlines regularly describe brutal drug-related violence.
"It is evident that we are not facing common criminals," Calderon said Friday. "We are facing true terrorists that have crossed all the limits, not only of the law, but also of common sense and respect for life."
Analysts said the attack could be connected with rival gangs seeking revenge, or the casino's owners could have been targeted for not paying extortion fines. But no matter what sparked the attack, analysts said it had a clear goal: Creating widespread fear.
"Without a doubt, what this act and others like it are trying to do is provoke terror in the population," said Jose Luis Pineyro, a professor at the Autonomous Metropolitan University in Azcapotzalco, Mexico.
"Of all the similar events, this has the most impact, not only because of the number of victims, but because it seems like they were trying to have the largest number of victims possible," he added.
Criminal organizations are using terrorism to challenge the government's security strategy and pressure people who have been protesting against violence, according to Jorge Luis Sierra, an expert in armed groups.
"There are various indications that drug trafficking and organized crime are laying the groundwork to put pressure on society and on the state, and given the larger military and police presence, they are resorting to terrorism," Sierra said.
The attack and others like it show failures in Mexico's military intelligence, Sierra said.
"As long as they haven't resolved problems of this nature in the security policy, the state, the government and society are going to be living in a very vulnerable situation," he said.
In the past three years, Nuevo Leon state -- located in northeastern Mexico -- has seen an increase in violence due to clashes between the Gulf Cartel and the Zetas gang over control of drug-trafficking routes to the United States.
Two mayors were assassinated in 2010. Last month, four civilians were injured when two grenades were thrown at a prison in Apodaca.
Monterrey, the state's capital, is a key industrial hub and Mexico's wealthiest city.
Since 2008, the government has stepped up the military's presence in Nuevo Leon as it tries to crack down on crime. It sent more troops to the state last November.
On Friday Calderon pledged to increase the presence of federal forces in Monterrey and northeastern Mexico to "restore to the people of Nuevo Leon the peace that has been lost."
In addition to the 1,500 troops heading to Monterrey, 1,500 federal police will be deployed to Nuevo Leon in the next several weeks, the state's public safety secretary told reporters Friday.
Thursday's attack has also drawn more scrutiny of the region's casinos. Authorities said Saturday that they had seized or blocked 2,800 slot machines at nine casinos under suspicion that they entered illegally.
More than 34,600 people have died since Calderon announced a crackdown on cartels in December 2006, according to government statistics. Other reports have listed a higher toll. The latest Mexican government tally was released in January.
CNN en Espanol's Krupskaia Alis and journalists Javier Estrada, Mauricio Torres and Victor Badillo contributed to this report.