The 2012 murder rate in Chicago has reached 500, the highest in four years and surpassing New York City, which stands at 414, according to police officials.

Authorities say the two American metropolises have shown a sharp contrast, even though the Big Apple has three times the population as the Windy City.

Police commissioner Garry McCarthy issued a statement on Friday calling the milestone a "tragic number that is reflective of the gang violence and proliferation of illegal guns that have plagued some of our neighborhoods".

But the police department went back and forth on Friday, first verifying the 500th killing, then backing off and saying an earlier death was still being investigated.

By late Friday, police confirmed 40-year-old Nathaniel Jackson had become the 500th homicide victim when he was fatally shot in the head outside a convenience store on the city's West Side.

Chicago, which is plagued by gang violence, had a total of 422 homicide cases last year, while the highest rate recorded was 512 in 2008.

The rise in homicides has frustrated Mayor Rahm Emmanuel, who vowed to make the city's streets safer on taking office in May 2011.

Commissioner McCarthy attributed the 18 percent rise to gang violence and said it was "unacceptable".

He blamed the violence on the rise of new factions that are vying for control of turf on the city's south and west sides.

McCarthy also said that 80 percent of the homicides were gang-related and 80 percent of the victims were African-American, though they only make up 33 percent of the city’s population.

"We're doing what we can do and it's working," McCarthy said, who added that Chicago faces a larger illicit gun problem than either New York or Los Angeles, the first and second-largest US cities.

After mounting criticism of Emanuel and McCarthy earlier this year, the police chief announced a shakeup of his department, transferring some police managers to other districts to bolster the battle against gangs.

Source: Agencies