ROCHESTER, N.Y. -- A gunman shot into a crowd that gathered outside the Rochester Boys and Girls Club after a basketball game, killing three people and wounding four others in what Gov. Andrew Cuomo called "a deplorable act of violence."

The drive-by shooting happened at about 11:20 p.m. Wednesday as people milled about outside the club, which is across the street from a school. Police said there was no problem at the club before the shooting.

"A fun and peaceful basketball tournament at the Boys and Girls Club ended with laughing as people walked home, but soon turned into a bloodbath because someone thought it was OK to open fire into the crowd," Mayor Lovely Warren said at a news conference Thursday with Police Chief Michael Ciminelli.

Officials have not yet released the names of the victims. The injured, all men in their 20s, have gunshot wounds that don't appear to be life-threatening, police said.

"Local authorities are working to bring the perpetrators of this hateful act to justice, and my administration stands ready to assist them in any way possible," Cuomo said in a statement.

A $10,000 reward was offered Thursday for information leading to the arrest and conviction of those responsible.

The mayor and police chief warned against retaliation, urging witnesses and others to report anything they know to police.

"We understand emotions run high," Ciminelli said. "More violence is not the answer to a violent act."

Warren said the shooting followed a "peace rally" earlier in the day that involved the city's Pathways to Peace program intended to discourage the use of violence in settling disputes.

"Hours later, three young men are dead and four more are wounded," Warren said. "Two of the young men who were killed last night were engaged in our Pathways to Peace program: Young men who were trying to turn their lives around. Young men who had promise and who we believed we could help and we could save from this culture of violence."

A large crowd gathered early Thursday near the scene of the shooting as family and friends of the victims consoled each other.

Police put out a call for surveillance or cellphone video, promising anonymity if requested. Ciminelli said about 100 people had been at the basketball game and an estimated 25 to 30 were still outside the club when the shooting erupted.

He declined to discuss a possible motive.

"We are bringing every resource that we have to bear on this," he said. "We will run this down and find out who did this. This was an outrageous act. We intend to find out who did it and bring them to justice."

The executive director of the Boys and Girls Clubs of Rochester, said the shooting happened about 20 minutes after the club-sponsored basketball game ended.

"The safe haven for our members of the Boys and Girls Clubs of Rochester has been compromised by this horrific incident" Dwayne Mahoney said in a statement.

He expressed hope "this heinous crime will be quickly solved."