At least eight people are dead and 101 wounded after a grenade attack shattered Mexican Independence Day celebrations Monday in the western city of Morelia.
Two grenades exploded just before midnight as people gathered in the centre of Morelia, capital of the state of Michoacan, said local officials.
Citing witness reports, Michoacan's governor said it appeared someone launched several grenades into the crowd as he was delivering the traditional "grito," or shout for independence.
"Without a doubt, we believe this was done by organized crime," Leonel Godoy told Mexico's Televisa network.
Michoacan has experienced a spike in violence after Mexican President Felipe Calderon, who took power in 2006, started to crack down on drug trafficking and related gang activity, reported Agence France-Presse.
Soldiers sent to state
Calderon condemned the attack and pledged Tuesday to redouble efforts against organized crime. He also sent thousands of soldiers to the state, saying in a televised address that the attack demands a response by the armed forces.
"These clandestine acts were clearly attacking our national security, committed by true traitors who have no respect for others or for the country," said Calderon.
Calderon has deployed more than 25,000 soldiers nationwide since he took power to combat organized crime, yet many of Mexico's criminal networks have been slaying their rivals in increasingly large numbers and publicly dumping beheaded corpses as expressions of their power.
24 bodies found in park
A particularly grisly mass murder was uncovered last Friday when 24 bodies, shot execution-style, were found in a national park outside Mexico City.
The attack Monday was one of the boldest yet, targeting the cherished independence celebrations that millions of Mexicans observe to commemorate the beginning of their 10-year war of independence with Spain in 1810.
Morelia's Independence Day parade scheduled for Tuesday has been cancelled, said Godoy.
A state official identified the explosives used in the attack as military fragmentation grenades, which are illegal for civilians. Authorities had still not identified any suspects or made any arrests, said the official, who asked not to be named.