CHICAGO - A series of gun attacks overnight in Chicago left four men dead, following a shooting at a South Side park that wounded 13 people this week, police said on Saturday.

The latest violence came as the city struggled to respond to a rash of street violence.

Chicago Mayor Rahm Emanuel returned home from Washington, after cancelling meetings there, and spoke at a prayer vigil on Friday night where he urged witnesses to Thursday's park shooting to come forward.

"We cannot allow children in the city of Chicago and we will not allow children in the city of Chicago to have their youthfulness, their optimism, their hope taken from them," he said at the vigil. "That's what gun violence does."

Chicago has one of the worst homicide rates in the country, with more violent crime than such places as New York and Los Angeles. The city's police department had been claiming success in stemming the violence with a strategy of flooding 20 high-crime neighborhoods with officers.

The four men killed overnight were shot in separate incidents between 6:15 p.m. on Friday and 3 a.m. on Saturday, said Chicago Police Department spokesman Officer Mike Sullivan.

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