CHICAGO -- Illinois Governor Pat Quinn on Tuesday proposed a state ban on assault weapons in the aftermath of the July 20 movie theater massacre in Colorado in which a former graduate student is charged with killing 12 people with guns including a semi-automatic rifle.

Quinn, a Democrat, called himself a "strong supporter" of the constitutional right to bear arms, but said in a letter to state legislators that the proliferation of military-style assault weapons undermines public safety.

"There is no place in the state of Illinois for weapons designed to rapidly fire at human targets at close range," said Quinn, who also proposed a ban on high-capacity ammunition magazines.

States including California, Connecticut, Massachusetts, New Jersey and New York have similar bans in place, Quinn said. A nationwide ban on certain semiautomatic rifles expired in 2004.

Sitthixay Ditthavong / AP, file Illinois Gov. Pat Quinn's proposal comes at a time when the homicide rate in Chicago has drawn national attention because of a 31 percent increase through July 20 compared with last year.

Poll: Views on gun laws unchanged after Aurora theater massacre

Illinois, the only state without a law permitting people to carry concealed weapons, has Democratic majorities in the legislature. But Quinn's assault weapons ban proposal likely would face obstacles from legislators outside of Chicago.

Suspect James Holmes, who seemed dazed and unengaged in court last week, on Monday appeared alert and attentive as a judge told him he faced 142 separate felony charges. NBC's Mike Taibbi reports.

The earliest the issue likely would be considered by the legislature is November, according to Brooke Anderson, a spokeswoman for the governor's office.

Speaking to NBC station WEEK, Republican State Senator David Luechtefeld accused the governor of trying to take political advantage of the theater shootings.

More news from NBC station WEEK

The man charged in the Colorado shootings, James Eagan Holmes, was armed with a Smith & Wesson M&P .223 semi-automatic rifle, similar to an AR-15 assault rifle, along with other firearms. He was charged on Monday with 24 counts of first-degree murder and 116 counts of attempted murder.

Prosecutors pursue two-track strategy against Colo. massacre suspect

The U.S. Congress is not expected to make any changes to national gun laws in the near future, political analysts say.

Slideshow: Shooting at Batman screening in Aurora, Colo. Ted S. Warren / AP As many as 12 people were killed and 50 injured at a shooting at the Century 16 movie theatre in Aurora, Colo. early Friday during the showing of the latest Batman movie. Launch slideshow

Quinn's proposal was outlined in a message in which he sent back to the legislature with amendments a bill that would allow state residents to buy ammunition through the mail. Legislators can decide to accept or reject his changes.

His proposal comes at a time when the homicide rate in Chicago has drawn national attention because of a 31 percent increase through July 20 compared with last year.

NBC station WEEK contributed to this report.

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