By Keith Coffman

AURORA, Colo. (Reuters) - Gun control activists staged a vigil in a Colorado park on Friday to remember those killed a year ago in a shooting rampage in a suburban Denver theater, as a gun rights group rallied nearby to protest what they called the exploitation of the tragedy for political gain.

The competing demonstrations on either side of the gun control debate took place about a quarter-mile apart in the suburb of Aurora's sprawling, picturesque Cherry Creek State Park, but there was little interaction between them.

At the anniversary vigil, organized by a gun control group co-founded by New York City Mayor Michael Bloomberg, activists and community leaders called on Washington lawmakers to pass legislation aimed at reducing gun violence as supporters held placards reading "No more names."

At one point, a handful of gun rights supporters stood outside the vigil of around 50 people, quietly holding signs in protest. At least a dozen uniformed Colorado State Patrol officers kept watch.

"You have Mayor Bloomberg politicizing this event and this is our answer to that," said Danielle Thompson, spokeswoman for Rocky Mountain Gun Owners. "We believe in putting the tools of self-defense in the hands of law-abiding citizens while Bloomberg's solution is to restrict and ban guns."

Other pro-gun activists wore orange hunting caps with the National Rifle Association logo or carried signs that read: "Aurora was a tragedy, Bloomberg is a travesty," and "Mayor Bloomberg mind your own business, not Colorado's."

Twelve people were killed and 58 others wounded on July 20, 2012 when a gunman opened fire during a midnight screening of the Batman film "The Dark Knight Rises" at a movie theater in Aurora. A dozen others suffered non-gunshot injuries in the ensuing pandemonium.

Former University of Colorado graduate student James Holmes, 25, has been charged with multiple counts of first degree murder and attempted murder. He has pleaded not guilty by reason of insanity, and prosecutors have said they will seek the death penalty if he is convicted.

State Representative Rhonda Fields, who spoke at the memorial vigil organized by Mayors Against Illegal Guns, called the counter-rally by gun rights advocates "insensitive and rude."

"They are re-traumatizing the victims as they try to remember their loved ones," she said.

The memorial was attended by family members of people killed in the theater rampage and of shooting victims of the massacre at Sandy Hook Elementary School in Newtown, Connecticut, last December. Among them was Tom Sullivan, whose son Alex was killed in the theater on his birthday.

"I now measure my time by Fridays," Sullivan said, referring to the day of the shooting. "It has now been 52 Fridays since Alex was taken from us by gun violence."

Sullivan praised Colorado lawmakers for passing new gun legislation following the shootings in Aurora and Newtown. The laws ban ammunition magazines that hold more than 15 rounds and require background checks for private gun sales and transfers.

Participants later planned to read names of thousands of gun violence victims from across the country, ending at 12:38 a.m. on Saturday morning, the moment gunfire erupted in the theater.

(Reporting by Keith Coffman; Writing by Dan Whitcomb; Editing by Cynthia Johnston and Chizu Nomiyama)