Calderon traveled to Monterrey with his wife and several Cabinet ministers. They laid a huge green wreath at the site of the charred casino, the letters "Bingo" and "Sports Book" on its broad red facade contorted by heat.
President Obama also condemned the "barbaric and reprehensible" attack.
Much of northeastern Mexico has been besieged for a year and a half by fighting between the Gulf cartel and former allies known as the Zetas.
The bloodshed has been especially shocking in Monterrey.
Hector Esquivel, 35, a valet parking attendant at the Casino Royale, had finished work half an hour before Thursday's attack. He got a job at the casino after the bar where he had been working received extortion threats.
"I came over here thinking it would be more calm, with the older people," he said. "It turned out worse. This is the dark side of Monterrey."