Mexican authorities say more than 40 people have been found dead inside a casino in the northern city of Monterrey that was set on fire by armed assailants Thursday.

Adrian de la Garza, the attorney general for Nuevo Leon state, told reporters more bodies could be found as crew dig through the burned out rubble of the Casino Royale. Monterrey is the capital city of Nuevo Leon.

Witnesses say several gunmen burst into the casino and doused the premises with gasoline before setting it on fire. Many of the victims were found inside the casino's bathrooms, where they fled to escape the gunmen.

Mexican President Felipe Calderon condemned the attack as an “abhorrent and barbaric act of terror” in a message on Twitter.

Casinos and other businesses have been targeted by drug cartels demanding protection money.

Drug-related violence has been on the rise in Monterrey, a city of four million people once seen as a safe and prosperous city.

More than 41,000 people have been killed since Mr. Calderon launched a crackdown against the country's drug cartels beginning in late 2006.