Flanked by members of his security Cabinet, the president stood near the bloodstained spot of one of the two attacks and said the explosions would only motivate the government to redouble its efforts against a growing crime wave.

Civilians and policemen help the injured at Morelia's main square September 15, 2008. Explosions ripped through a crowd of people celebrating Mexican independence day, killing at least three revelers and wounding about 50, the Michoacan state government said. [Agencies]

Both he and the first lady also visited the dozens of injured at hospitals. Among them was a 13-year-old fighting for his life.

The attack on the general public appeared to represent a new tactic in the intensifying war between drug cartels and federal authorities. Previously, most violence, including assassinations, massacres and beheadings, targeted rivals, police or soldiers.

Witnesses said a man in his late 20s dressed in black threw a grenade, then begged for forgiveness as another grenade exploded nearby. They provided enough details for a composite sketch, which was distributed to police agencies in surrounding states, according to Michoacan Attorney General Miguel Garcia.

He said authorities have received new threats and have had to evacuate at least one building as a precaution. He did not elaborate.

Garcia announced a 24-hour hotline to handle the flood of anonymous tips, many of which he called unsubstantiated, and urged the public to come forward with any photos or video taken during the attacks.

The federal Attorney General's office, which is leading the investigation, said authorities are looking into illegal arms charges, but do not yet have enough evidence to say for sure that drug cartels were responsible. No arrests have been made and officials declined to say if anyone had claimed responsibility.

Mexicans said the attack made them feel more vulnerable than ever.

"Before we were safe, but now we walk around afraid," said Sandra Munoz, 22, who stopped in a Morelia church on her way to work to light a candle for the dead. "Everyone is unsafe now."