Mexican authorities say they are seeking seven more suspects in an arson attack that left 52 people dead at a casino in the northern state of Nuevo Leon.

Officials made the remark Tuesday as five others in custody were presented to the news media. Authorities say the five are alleged members of the Zetas drug cartel and have confessed to involvement in the attack at the Casino Royale in the state capital, Monterrey.

Last Thursday, armed men carrying a flammable liquid burst into the casino and set it on fire. Many of the victims were found inside the casino's bathrooms, where they fled to escape the gunmen, but were instead trapped by smoke and fire. Police are investigating whether the attack was linked to extortion.

Mexican President Felipe Calderon condemned the violence as barbaric and called it the worst attack on innocent civilians in Mexico in a long time.

Mexico has offered a $2.4 million reward for information leading to the arrest of the suspects.

Organized and drug-related crime in Mexico has killed about 41,000 people since late 2006, when President Calderon took office and began a military campaign against his country's drug cartels.