Responding to Thursday's devastating terror attack at a Monterrey casino, Mexican President Felipe Calderon has demanded that the U.S. crack down on illegal trafficking of weapons across the border into Mexico. Government officials said the attack was carried out by members of the Zetas drug cartel, who allegedly targeted the casino because the owners had not paid them a sum of money they had demanded. Monterrey, 140 miles from the Texas border, has been bombarded by rival drug gangs who routinely attempt to steal from its casinos. Calderon urged Congress to crack down on weapon trafficking from the U.S. border into Mexico. "We're neighbors, we're allies, we're friends, but you are also responsible," Calderon said. Attackers bombarded the casino with gunfire and grenades before starting a fire, killing at least 53 people.