Updated

Homicides in Chicago spiked by 60 percent during the first three months of the year despite an increase in police resources in some of the city's most dangerous neighborhoods, according to new police crime statistics.

The Chicago Police Department data showed that nonfatal shootings also rose sharply in the first quarter compared with the same three months in 2011.

Chicago police and Mayor Rahm Emanuel say the city has increased efforts to combat gang crime, including adding officers and other resources in trouble spots such as the Englewood neighborhood on the South Side. Police blame much of the violence on the city's more than 70 active gangs and their tens of thousands of members. The mayor has urged residents to take a stand against gangs in their communities.

The police statistics show 120 homicides from Jan. 1 through April 1, compared with 75 over the same period in 2011.

Factors contributing to the rise could range from lingering economic woes and high unemployment to the unseasonably warm weather that brought more people outside, increasing the chances of conflict and crime, said Jens Ludwig, director of the University of Chicago's Crime Lab.

He cautioned that it is risky to draw hard conclusions from three months of data or even a full year's worth of figures, noting that the overall trend in Chicago has been toward lower murder rates.

"Since the early '90s it's been going down, but there are years when you see these sorts of upward blips around the larger trend," Ludwig said. "... We wouldn't necessarily want to jump to conclusions too much on the basis of one quarter's data."

All six other crime categories tracked in the police statistics were down for the first part of the year, including a 15 percent decline in sexual assaults and a 9 percent drop in robberies. Car thefts declined 16 percent to 4,081.

Of the 120 homicides, 101 involved shootings, police said.

Chicago has for years tried to cut off the flow of guns. It has what city officials call the strictest handgun ordinance in the United States. The measure bans gun shops in Chicago and prohibits gun owners from stepping outside their homes, even onto their porches or in their garages, with a handgun.

The City Council raced to pass the restrictions in July 2010 just days after the U.S. Supreme Court struck down an outright ban on handguns that Chicago had for 28 years.

Mayor Rahm Emanuel has pushed for other restrictions, including a bill working its way through the Illinois House that would require handgun owners throughout the state to register their weapons.

Ludwig said that could give police an important tool to potentially track weapons beyond their initial sale at legal gun shops as they change hands on the currently unregulated secondary market.

"Registration gives you a way to hold gun owners accountable for what they do with their guns," he said. "... Everything that happens after the first purchase in most places is just invisible. Nobody's got to keep track of anything legally."

The bill, however, faces hurdles and has set off another round of skirmishes over gun control in Illinois.

There is also a legal challenge to a ban on assault weapons in Cook County, which includes Chicago.

Gun advocates are pushing hard in the Legislature and the courts to bring concealed carry to Illinois, the only state that doesn't let gun owners go out in public with their weapons hidden.